Here are a couple of applications that you may find useful.
I compiled these statically in Puppy Linux, I've added missing lib files libjpeg.so.7 and libpng12.so.0 to the applications install directory
which are loaded by a script, this way it will not pollute the file system, tested and working in Porteus-XFCE-v3.2rc3-i586
Selective colour. Saturation control.
Photoshop plugin and standalone application.