IEC 60204-1 reserves RED exclusively for emergency stop actuators, and explicitly forbids RED on START/ON pushbuttons, while STOP/OFF actuators must not use GREEN [S3][S4]. The preferred palette for both START/ON and STOP/OFF is WHITE, GREY, or BLACK, with WHITE preferred for start and BLACK preferred for stop [S1][S3][S4].
GREEN is permitted on START/ON (not preferred) and is banned on STOP/OFF and on combined start/stop pushbuttons [S1][S3][S4]. The "green means go, red means stop" mental model that lives in road traffic and consumer electronics is not the rule inside a control panel governed by IEC 60204-1, and specifying against the standard creates a real compliance defect.
The IEC 60204-1 color matrix, function by function
For START/ON actuators, IEC 60204-1 lists WHITE, GREY, BLACK, and GREEN as permissible, with WHITE as the preferred color, and RED is explicitly forbidden [S3][S4]. Schneider Electric restates the same rule: "GREEN is also permitted. RED shall not be used" for START/ON [S4]. AWC's reference table gives the identical reading: "GREEN may be used; RED must not be used" for START/ON, with WHITE preferred [S1].
For STOP/OFF actuators, the standard lists BLACK, GREY, and WHITE (BLACK preferred) and permits RED, but GREEN is forbidden [S1][S3][S4]. Schneider phrases it bluntly: "RED is allowed. However, GREEN is totally forbidden" [S4]. The same matrix also notes that when WHITE and BLACK are paired on the same panel to distinguish start from stop, WHITE must be assigned to START/ON and BLACK to STOP/OFF [S4].
For combined start/stop pushbuttons (one actuator toggling between the two states), only WHITE, GREY, and BLACK are acceptable, and YELLOW, GREEN, and RED are all excluded, with the only carve-out being a non-pushbutton actuator that doubles as both emergency stop and normal stop [S1][S3][S4]. For hold-to-run / jog actuators, the same WHITE-GREY-BLACK restriction applies and again YELLOW, GREEN, and RED are excluded [S1][S3].
Why RED is locked to emergency stop, and what changes for combined E-stops
IEC 60204-1 mandates that EMERGENCY STOP / OFF actuators are identified by the color RED, with exceptions allowed only when RED is not available, in which case other means must reliably identify the actuator function [S4]. The AWC reference table reinforces this: "The color RED must be used for emergency-off actuators" [S1]. Safety-products.de narrows the combination further: emergency stop uses RED, or a RED button on a YELLOW background, and that combination is the only place the standard allows a two-color treatment [S3].
When the same actuator is used for both emergency operation and normal STOP/OFF, it must still be RED, with the same exception rule if RED is unavailable [S4]. This is the technical reason a "big red mushroom" on a machine is reserved for E-stop duty, and why reusing that mushroom for a routine stop is a spec error, not a styling choice. For a practical reference on the hardware side, see the emergency stop button page, which covers the mechanical and contact-block requirements that pair with the color rule.
Where GREEN, YELLOW, and BLUE are allowed, and where they are not
GREEN is reserved by the standard for functions indicating a safe or normal operating condition, which in practice means indicator lamps and pilot lights, not pushbutton caps on a stop button [S1][S3]. A GREEN pushbutton on START/ON is a permitted exception; a GREEN pushbutton on STOP/OFF is a direct violation of IEC 60204-1 [S1][S3][S4]. YELLOW is reserved for warning or abnormal status, again pointing to indicators rather than operating pushbuttons [S1][S3]. BLUE is reserved for functions of urgent significance and is the required color for RESET pushbuttons along with WHITE, GREY, and BLACK, and GREEN is forbidden on reset [S1][S3].
This is why a panel that flashes a GREEN pilot light to say "machine running" and a YELLOW pilot light to say "fault" is following the rule, while a YELLOW STOP button or a GREEN reset button is not. Pilot lights follow a parallel but distinct set of color rules; the pilot light reference page lays out the indicator-side specifics that sit next to these pushbutton rules.
Decision matrix: pick the cap color by function, not by habit
Function-by-function, the allowed and forbidden colors under IEC 60204-1 line up as follows. START/ON: WHITE (preferred), GREY, BLACK, GREEN permitted; RED forbidden [S1][S3][S4]. STOP/OFF: BLACK (preferred), GREY, WHITE, RED permitted; GREEN forbidden [S1][S3][S4]. Combined START/STOP toggle: WHITE, GREY, BLACK only; RED, YELLOW, GREEN all forbidden (narrow exception for non-pushbutton dual emergency actuators) [S1][S3][S4]. Hold-to-run / jog: WHITE, GREY, BLACK only; RED, YELLOW, GREEN forbidden [S1][S3]. EMERGENCY STOP: RED required (or RED on YELLOW background), no GREEN, no other color as a substitute unless RED is unavailable and a reliable alternative identifier is used [S1][S3][S4]. RESET: BLUE, WHITE, GREY, BLACK only; GREEN forbidden [S1][S3].
Rockwell's NEMA-aligned guidance lands on the same conclusion: "For NEMA Start or On push buttons green color cap is preferred with a flush head operator" is treated as a NEMA convention rather than an IEC mandate, and RED is still not allowed on START/ON under either regime [S8]. NEMA and IEC differ on the GREEN-for-start preference but agree on banning RED on start and GREEN on stop, which is the cross-standard core of the rule.
When the panel can break the "red is stop" habit
There are two narrow cases where RED appears on a non-emergency actuator. First, a non-emergency STOP/OFF pushbutton is allowed to be RED as long as it is not co-located with an emergency stop button, because the proximity would create ambiguity about which RED actuator is the safety-critical one [S1][S2]. Second, a combined emergency-and-normal-stop actuator must be RED regardless of how it is labeled, because the emergency function dominates the color choice [S4]. The AWC table lists RED as permissible for STOP/OFF in the same color row, with the same proximity constraint echoed in the Medium walkthrough of the standard [S1][S2].
For STOP/OFF on most industrial panels, BLACK remains the cleanest default and avoids the proximity problem entirely [S1][S3][S4]. A BLACK stop cap on a WHITE start cap is the most contrast-friendly pairing and is the explicit example the standard calls out for distinguishing start from stop by color alone [S4].
Symbol, engraving, and shape coding as the tie-breaker
When two pushbuttons on the same panel must share a color, IEC 60204-1 requires a supplementary coding method, typically engraving, symbol, shape, or position, so the operator can still tell the functions apart [S1][S3]. Schneider's restatement of the rule notes that color codes are about priority of action, with flashing reserved for attracting attention, which is why the standard layers symbol on top of color rather than relying on color alone [S4].
The standard's own list of engraved symbols covers start, stop, on, off, up, down, left, right, reset, push-button change, caution, lock, unlock, and ready-for-operation, so there is a symbol for every common pushbutton function the color rules describe [S3]. In practice, a flush WHITE start cap engraved with the "I" (start) symbol and an extended BLACK stop cap engraved with the "O" (stop) symbol is the most spec-clean combination on a non-safety panel.
Practical spec checklist for a compliant pushbutton station
Use WHITE for START/ON as the first choice, with GREY, BLACK, or GREEN as alternates, and never use RED on a start button [S1][S3][S4]. Use BLACK for STOP/OFF as the first choice, with GREY or WHITE as alternates, permit RED only when no emergency stop is co-located on the same station, and never use GREEN on a stop button [S1][S3][S4]. Reserve RED exclusively for the E-stop actuator, paired with a YELLOW background where the mechanical layout calls for it [S1][S3][S4]. For RESET, pick BLUE first, then WHITE, GREY, or BLACK, and avoid GREEN [S1][S3]. For indicator lamps, follow the parallel color logic in the pilot light rules so the panel reads consistently under stress, with the pushbutton pilot light reference as the cross-check.
For the E-stop hardware itself, the emergency stop page covers the safety-contact and mechanical-latch requirements that sit behind the color rule, and it is worth pairing the color spec with that hardware spec at the same time so the panel passes both the IEC 60204-1 visual check and the functional-safety check. A second cross-check is the coding machine reference, which covers the symbol-and-engraving side of the supplementary coding rule.
Trackable signals to watch: any future revision of IEC 60204-1 that adjusts the GREEN-on-start permission, and any harmonization note between IEC 60204-1 and IEC 60073 that changes the indicator-lamp color map. Both would force a re-spec of existing panel BOMs, so a one-line check on the current edition clause numbers during procurement is the cheapest insurance against a silent standard drift.
This topic is covered further in Conveyor Chain Selection for Agriculture Machinery: Pitch, Series, and Attachment Logic.