>The Standard GIMP Color Selector
You can change the color manually by clicking on a hue in the spectrum color field to the right, and then dragging the cross in the large color box on the left to the exact color you want. If you want a specific RGB (Red, Green, Blue) or HSV (Hue, Saturation, Value) color, type the exact value in the HSV or RGB parameter fields or drag the sliders to specify a color.
The H (hue) channel is displayed in the color fields by default when you open the Color Selection dialog. However, you can choose to search in another channel for the color you want. It can be very useful to change the channel to S (saturation) or V (value) when you're searching for a specific color. The color spectrum will be displayed in a quite different way by doing this and you might find it more useful.
In the bottom of the dialog you will find the current color specified as a hexedecimal triplet. The function is targeted at web developers — to get the color code into your HTML document simply select it and paste it in with your middle mouse button. If you are using GIMP for Windows you must use Ctrl+C and Ctrl+V to achieve the same result.