MV lenses?!??!

Regarding MV lenses. I've used them a few times, and have several packages on hand, but have noticed that the clear ones turn yellow with age. This may be over a period of a few years. Anybody else had this experience? I asked the local railroad model shop guy about it, he said yeah, they do yellow. Don't know if this applies to other similar products.

Ahh.. thanks for the responses, guys!

You can also use sequins for reflectors in lights.

Just this afternoon, while I the local craft shop, I saw these little bags of small, facetted clear gem-lihe things that can be glued the things, I quess. These gem-thingys have a flat back and are mirrored under the clear plastic gemstone. I was thinking these might makegood light lenses especially for small scale A/C. The smallest gem is about 2mm in diameter.

MV lenses come in clear, red, blue, green, and black in various sizes.
They can be purchased at model RR shops.

http://users.dwx.com/kingkgk/images/mvlens.jpg

You can check out their products here: http://www.walthers.com/exec/page/manuinfo/v516

I asked this question a long time ago and now, I desperately need an answer. What are M.V. lenses? What do they stand for? Do they come in different sizes and colors? Most important of all, where do i get them? ANY (and I mean ANY ) reply would be highly appreciated. Thank you guys!