There's two "lines" of pastels- VPI and Lemon. I never really "got it" until I was able to actually hold a VPI in my left hand, and a Lemon in my right hand (thanks Adam!). The Lemons seem to have a brighter yellow and a sharper black in their patterns, with a sharp contrast between the two colors. VPI seem to have a duller yellow with more blushing around the back and neck areas.

As far as fading out, I don't think there's many pastels out there that won't fade their bright yellow as they get older. I think I've seen that the lemons hold more yellow, while the blushing on VPIs patterns really come out as they get older.

Both of those lines are compatible, and both lines will produce really really nice pastels and really really dull pastels. My advice to you is to try to see each of the lines in person before you buy, and just decide on which one you personally like better!