[mkgmap-dev] Background Fill Polygon

Etrex and Gpsmaps units (maybe others too) display the map background in yellow, this is not good for contrast and makes reading the display difficult while in forest or other places with quickly changing light conditions between sun/shadow. One can define 0x4b polygon color in typfile, with white or greay to remedy the situation. However this makes the gps draw the background twice and reduces performance when scrolling the map. Would it be possible to have mkgmap fill up any area where there is no polygon defined? It should be customizable which polygon to map instead (0x01 would probabely work well for people not using typfiles). It simply should not be 0x4a or 0x4b.