It seems to me that the backgrounds of these use the transparent color of CSet 0 automatically, however, you can set the background color for any other text on the subscreen. Should this be something put into the Misc colors section? So, say for instance, you have white text, and you are using the transparent color on CSet 0 also as white, it just shows up as a big white block.
Allow me to illustrate:
http://www.filespace.org/bam200308/whiteblock.gif
