Erm, yeah I had this. The visor overlay is the little square in the bottom right of the helmet skin, and you have to paint that some colour (in LFS that colour is overlayed over a black visor but in 3DS it's just the colour on the skin, so visors can be very bright).
Hang on *loads 3DS*
I think the only thing I had to do was make sure that little square was coloured in in the bottom right (see a mesh template if you don't know what I mean).
Have fun experimenting and I hope it helps (if not post again or PM me and I'll see if I can help you more, but I warn you I am no 3DS expert )