The color is based on HTML and thus you can enter wither the color name or color code. For color name, 147 names are recognised and you can see the list here. For example, in the screenshots in the first post, I have used green as the color name. You can see the result in the screenshot.

If you want greater control over the shade of colour, you can use the hexcode. It is of the format #-red-green-blue, where each colour is defined by a two digit hexadecimal code. Or, you can get it easily from here.