Porsche in period commonly brush-painted matte fluorescent identification panels onto their works cars. Painting quality was not uniform, brush strokes were left plainly visible - utility was everything, finish irrelevant.
DCN
My immediate thought was fluorescent.
Two things to consider about fluorescent paints:
The effect doesn't generally photograph well (think of various Marlboro sponsored cars down the years)
In my experience (admittedly greater with screen printing ink than automotive paint), they're generally matt rather than gloss.
There's something very strange about fluo screen ink (and possibly brush applied paint?), it looks like it's going to be very thick, and opaque, but it's actually really very translucent and needs to be backed up with white for best effect (not generally a problem with late 60s Porsches!)
Richard