Not sure if it was different over the years, but mine (86) is actually a
white bulb (like all the rest of them) with a blue plastic lens that
covers it.  There was some trouble when the blue lens *tiny little
thing* fell out and I could barely get it back in there, but a blue bulb
wasn't required.  I recall also that my previous 89 was the same.

Hope this helps,

Greg
86 Westy
73 Thing