Color-Image-Generator is a project mainly written in PHP, it's free.
PHP script that generates an image filled with specified color.
Color Image Generator
This is a very simple ImageMagick-based script that generates an image of specified size, filled with the specified color (by hex code).
Image is displayed next to the form which defined the attributes. It is also possible to download the image by clicking on it.
In case when multiple colors are specified, the generated image will be filled with the first color and have a progressively smaller box for each of the additional colors.