With a button set to Effect in Steering Wheels > Button Effects, these drive it from the car rather than from your press.

• DRS. Lit when DRS is available or active.
• KERS and ERS Lap Deploy Limit. Covers KERS on F1 cars from 2009 to 2013, and the lap deploy limit on modern F1 cars.
• ERS Mode. Shows the current energy mode, such as Attack or Balance.
• Push to Pass. Lit while push to pass is available or running.
• Pit Limiter. Lit while the speed limiter is engaged.
• TC Active and ABS Active. Flash while traction control or ABS is actually intervening, not merely switched on.
• Ignition, Engine Start, and Ignition and Engine Start Combined for the starting procedure.
• Low Fuel Alarm. Lit when the low fuel warning is active.
• Value Increase and Value Decrease for buttons that step a setting up or down.
• TDM Toggle for Team Driver Mode.

Two game caveats worth knowing. TC Active needs the third party Dahl SimHub plugin in iRacing, and ABS Active is not available in iRacing at all because the game does not publish that telemetry.

Colours come from the button's own colour, which needs the Custom theme and is overridden by Universal Theme.