Are you repainting the walls or keeping them yellow? The two most popular suggestions for painting ceilings is to 1) paint them white or 2) dilute the wall paint 1/2 to 1/4 strength with white paint so you get a lighter version of the wall paint on the ceilings. Another suggestion I've read is to paint the ceiling the lightest shade on the same paint strip the wall paint was chosen from. Some like to paint the ceiling the same color as the wall or even a darker shade, but I think those options are probably for the more adventuresome or those who have knack or expertise in decorating.

It all seems to be a matter of taste.

You might want to post over at the Home Decorating thread for most suggestions.