As an engineer based in the UK, I claim no particular expertise, but think this is covered in NFPA79, Sect 13 'Operator's Control Station & Equipment'.
This mirrors the European Standard EN60204, section 10.
Briefly for (pushbutton function)/[indicator]
Red:
(Stop) / [Alarm or abnormal condition]
Green:
(Start) / [Running]
Yellow:
(Reset, suppress alarm) / [Caution]
Black:
US: Not used
Europe: Not specified
White:
US: (Any function not covered by above) /
[Normal condition]
Blue:
US: (Any function not covered by above)
Europe: Mandatory command to operator: change tool, etc.
Please note this is a general guide to get you going, no responsibility taken!
