[604] Fix for inverted text box colour in paletted modes
Detail: Turn defaultpalettes back off (cf. Colours 1.95) as this caused writable icons to be the wrong colour in low colour modes because the Wimp palette is not the same as the default palette tables which ColourTrans substitutes. Furthermore, in 256 colour modes deselected Filer icons had the wrong colour caused by an attempt to lookup a palette for a true colour mode - a test has been added for <= 8bpp should the option ever be enabled in future.