Windows forms : color dialog solid color only

After chekcing the options on the ColorDialog of Windows forms, I was wondering the difference between putting SolidColorOnly propertie to true or false (in other words what is a Solid color and what is not).

If you want to know what solid color means, then the question could be "What solid color means?".

A solid color means that all pixels have the same color. For a single pixel it doesn't make much sense, but a larger area can be colored with some kind of raster consisting of pixels in more than one color. When such area is viewed from a distance, it almost looks like another color.

Edit: Picture of windows color select dialog in 256 colors