The best way to isolate a multi colour figure from a multi colour background is to carefully draw around it with the lasoo tool.(Thats the one next to the magic wand in apesnaters diagram).Once you join back up with your starting point you have made a "selection" of the figure.As its the background you want to play with go to the drop down menu "selection - inverse".Now go to edit-fill,and you can fill it with your foreground colour,or play around with it anyway you wish without affecting the figure.