The values for the resolution are set in the option style file:
http://www.mkgmap.org.uk/svn/wsvn/mkgmap/resources/styles/default/options

In the default mkgmap settings are
levels = 0:24, 1:22, 2:20, 3:18, 4:16

By coincidence today I discovered a glitch in mine,
levels = 0:24, 1:23, 3:22, 4:21, 5:20, 6:18, 7:16 but it should be
levels = 0:24, 1:23, 2:22, 3:21, 4:20, 5:18, 6:16

Maybe this is also the reason why they dont respond as expected in your map, because my settings differ from the default mkgmap settings. The colours are set in the typ file btw, so you can play with them too to make it appear the way you want.