InstantPhotoColor is a free image editor ideal for colorizing black and white images. It can also create great effects on colored images. Its interface basically consists of an editing window where you can freehand-paint over the loaded image without changing its lightness and texture.
It also includes two zooming buttons to reduce or enlarge its view, a slider bar that adjusts the brush size, and a color button for changing the brush color. If it is required, you can resize its window to expand its working area.
You can repaint any area even if it was already painted, and the original color is completely substituted with the new selected color.
Even though the program is free to use, it has some disadvantages; it supports different image formats (png, jpg, bmp, jpeg, tiff, tif, gif), but only allows you to save images with jpg or png format, besides it lacks an undo function to revert the changes made.
Finally, regardless of its simplicity, you can take advantage of it to add or change the color of your pictures without distorting them. No expert skills are required.