Either orange or with special coating.
The special coated bulb only lights orange when you use the indicator (bulb is usually used with transparent lenses).
Single
Bulb Instrument Lighting
12V/1,2W W2x4,6d, T5x20mm...
Bulb 12V 55W PK22s H3
Attention: Please do not...
Bulb Rear Light
Bulb 12V 21/5W BAY15d S25x47mm...