Go to Race Page -> Race Theme. There is a new button to Add Custom Color Theme:
When you click that, the custom editor will pop up with whatever set of colors you have set currently (the example below shows the default blue and orange):
There are 6 colors to pick – Background color, Font Color and then 4 colors used in various elements on the page. To change any of them, simply click on the square. This will bring up the color editor of the computer you are on. These screen shots show a Mac – PC’s and phones will be much simpler (not as good – get a Mac!) in terms of what they have.
If you are trying to match another website colors, you might want to look for the “Hex Value” (here is a website, here is another, here is another) used in the webpage. On the Mac, here is where you can edit the hex code:
Word of caution! Make sure your text shows up on your background. For example if you have a white background and pick yellow for header colors, then people will not be able to read the header.