http://packages.debian.org/wheezy/kolourpaint4 is a kde thing
as is
http://packages.debian.org/wheezy/krita which might be too big
http://packages.debian.org/wheezy/mtpaint appears to have a few (at least one) floating toolbar - the naming conventions or DISPLAY=:1 may have caught you/xephyr out for showing it all on a smaller screen.
I think
http://packages.debian.org/wheezy/rgbpaint is not a terrible place to start.
http://mtpaint.sourceforge.net/rgbpaint.html