rgbPaint is a very basic GTK+2.6 (or later) based program designed for
editing pixel based images. It is a fork of mtPaint 3.09.  It can only
edit and save RGB images to PNG, JPEG, or ICO files.  It can read PNG,
JPEG, TIFF, GIF, ICO, files and possibly others like TGA, PCX, and SVGi
if they are installed with your version of GTK+2.

WWW: http://mtpaint.sourceforge.net/rgbpaint.html