For the 8 y/o maybe BM Old Blue Jean #839:
http://www.benjaminmoore.com/en-us/paint-color/oldbluejeans

After trying a bunch of blues in DS's room we found that this one really works well, particularly with lighter colored furniture (birch)

For the 16 YO, I like this color:
http://www.benjaminmoore.com/en-us/paint-color/eveningdove

If you like lighter, this site has some subtle grey shades:
http://ths.gardenweb.com/forums/load/decor/msg060748449504.html

I like something like this for the 8 year old's color scheme:
http://www.benjaminmoore.com/en-us/paint-color/lighthouselanding

For 8 yo, looking for a denim blue wall color for a red-loving boy with basic red/blue plaid comforter and Pottery Barn red with bloe stripes drapes. For 16 yo, looking for a steel/cement color, we think, for a black, white, brushed aluminum decor. I don't know why but we can't seem to come close to a workable wall color. So looking for recommendations. Thanks.