Flush video memory does indeed work in dbc/enhanced, and it clears all the textures from your graphics card memory. You can make sure to use 'draw do front, and that default blue is probably still a backdrop. So also use backdrop off, as the backdrop constantly refreshes the screen. if you need some 3d objects to remain then you can make a set of plain objects that fills the whole screen with your images textured on those, and lock them to the screen
ZX Spectrum 48k Issue 3, Radio shack Tape drive, Rank arena 12" T.V. set.