I have to agree with the comments here. Most of my collection sits in open glass cubes next to a window. Although the blinds are kept closed and I keep Valks with color closest to the window there are days where sunlight is coming in, but I have not experienced any yellowing on any of my Valks (knock on wood...knock knock!). Mind you I have only been collecting since January 2008 so most of my stuff is fairly new, but never played with; only displayed. I think what initially drew me to the Yamato brand of Valks was the innovation and accuracy of the "toy". Since learning more about the hobby I have seen that models make the toys look like; well toys, but they are still magnificent to look at.