Phillips makes a bulb called "Silver Vision" that looks silver like the reflector when off, but flashes orange when activated. http://www.fosmo.com/
has a pic and ordering info under "Philips, Silver Vision indicator".
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E