You copy your avatar into paint
Use the eyedropper to select the color you want
Then click Edit Color to see the color codes

Then open the standard calulator
Under View, switch to Programmer mode
Then type in the Red: 167
With the number in, switch from Dec to Hex mode

It will give you the first two parts of the color code A7
You do this with all three colors and it puts together the full code
(The one shown on the image is for the Blue code)

This is how I do it, there could be other easier ways,
depending on if you have photoshop or some other program
I only have MS Paint to work it, so that's how I do it