first, make sure the background colour is positioned in the bottom right corner in the palette.
If this doesn't work, make the foreground act as an animation without it being animated. in the background definition, where you would normally put "type = normal", put type = anim actionno = 1
Then, at the bottom of the .def, add [Begin Action 1] #defines the Action Number 0,0,0,0,50 #Sprite Group, Sprite Number, X-Axis, Y-Axis, Ticks Set the first two digits to match your foreground piece. Don't touch the x/y-axis. Doesn't matter for how many tick you put it in.
If you want to add things behind the foreground, simply do the exact same thing, but be sure to position the backdrop BEFORE the foreground. Example: ;---------- [BG 0] #Backdrop type = normal spriteno = 0, 0 start = 0, 370 delta = 2, 2 mask = 0 velocity = 0, 0 tile = 1, 0 tilespacing = 0, 0