The sandstone sounds like it would look better than white, a little softer color variation. My first bear, a smaller one, I did black over green, the black along the fur made it look a little bigger, my second rug I did red inside on black as he was over 7 feet and didn't need any help.
I think if you include vacuuming the felt in your weekly housekeeping, you would not have a problem with dirt. It's just remembering to do it that is the issue. Also, some places seem dustier than others, I probably would not do a light color in my home, but we are one of the dusty ones it seems. Maybe I need to vacuum more....
