(1) Download a chart of "html color codes". It may take a bit of time until you find a chart you're happy with.
(2) Go to the color pallette you used to make your pie chart, and click on yellow as an example.
(3) Along with the color, you'll see a code that looks like: #ee0000. This is the html code number for that particular shade of yellow.
(4) Click and backspace the code to erase it.
(5) Type in a different code...let's say #99ffcc.
(6) Hit ENTER. You've just created the color Lt. Blue.