Colour changes

............Hi ....is there any thing special about modyfying the bit maps contained in .cab files? I'd like to change the colour of the GPS 500 to something other than the mid grey it now is. I can copy the .bmp files and change them in P/Shop but it does't seem to want to allow me to put the modified files in the .cab...is there some way to do this please?....thanks in anticipation...commoner 
