Spectrum Shift Paint is a neat little app for creating and playing with color-shifting animations.
You utilize your mouse with animated brushes to draw out an image; you can then add a variety of effects and colors to that image. From there, you can add different color shifting effects that are reminiscent of the backdrop from a 60's era Jefferson Airplane concert. There are several of these effects to choose from like Blackhole, Neutron Star, etc., and you can configure the speed and color variance you desire. There are also multiple GIF animations included for use as a background for drawing over.
Spectrum Shift Paint includes an export feature that enables you to export your animations for creating web pages powered by WebGL. Simply copy the exported pages up to the web to display them.