[mkgmap-dev] Map Background Colour

I am trying to set the background on my maps away from the standard "yellow-orage" colour, I am tried setting the colour of polygon 0x04b to white, and assigning it to layer 1, with no other polygons set to 1 there are all at level 2 and higher, when i look at the map in basecamp, the map background is now white, but all the other polygons have disappeared. the lines and points are still visible. What have I done wrong ? Gary