i am also interested in knowing how to change this. i think the splash looks brighter on stock bg because of the black menus.
Edit: found the images. they are in the framework-res.apk res/drawable-hdpi-v4 folder (on rooted/deodexed GB) and they are called:
overscroll_edge.png
overscroll_glow.png
extract those images, change colors, use Ninja Morph to put them in there, and they should change. i have NOT tried ninja morph yet b/c i am not sure if it works or not. some say yes, some say no.
