Painting colors, lightness, saturation, and so forth onto photographs can be great fun. If done correctly, it can also produce some very attractive, creative pictures. Akvis MultiBrush ($49, 10-day free trial) is a very basic image painting program that provides some nice tools, but they are limited and require skill to be able to use them.
MultiBrush's interface is clean and very simple. On the top are a handful of icons for opening or saving a file, printing, Undo or Redo; to the right, you'll find links to the online help and preferences. The toolbox to the left of the image window offers a limited group of painting tools, such as: Color Brush/Color Pencil, Eraser, History Brush, Clone Stamp, Chameleon Brush, Sharpen/Blur, Lighten/Darken/Saturation, and so forth. Among these, the most interesting is the Chameleon Brush, which is a specialized cloner for applying the luminosity of a source image onto a destination background, using the colors of the destination. That can create some interesting ghostly or otherwise artistic effects. A History Palette keeps track of your edits, for easy control over Undos. The History Brush doesn't really use this palette; instead, it is a selective Undo, restoring the area brushes to the original image.
Brush options are very limited. But more important, with no Selection or Masking tools, you have to have great hand/eye coordination to place precise brush strokes, for the best effect.
MultiBrush is also available as a plug-in for Photoshop-type programs, for the same price of $49. Or you can get both the plug-in and standalone editions for $69. While the MultiBrush standalone opens and saves JPEG, BMP, PNG and TIF files, the plug-in will support files native to the host program (such as PSD in Photoshop).
How useful and fun you'll find Akvis MultiBrush to be will be very dependent on how good you are at painting on a computer screen, and how demanding you are as a imager. Or, you can simply use it for fun doodling. We found it too limited for our tastes, but it might be just the ticket for what you want to do. The only way you'll know for sure is to try to the trial version on some of your own pictures. Or, if you're able to stretch your budget, take a look at Corel Painter Essentials, which is twice as expensive, but provides far more than twice the functionality.