Its very easy to add custom color scheme if you have primary knowledge of css and photoshop.
These are the steps.
1) Please open <theme-root>/styles/ folder and create another copy of closest matching color scheme. For example, If you want Red color scheme please create another copy of pink.css and name it as red.css.
2) Open red.css in your favorite editor and Find/replace color codes with your needed color. Means say you find #C95980 first , now in photoshop visualize this color and find matching color code for red color. Say you find it as #cc2127. Now instead of modifying only 1 occurrence find all #C95980 and replace them with #cc2127 via your code editor.
3) Repeat step 2 for all colors , there are around 3-4.
4) Upload this red.css file to <theme-root>/styles/ .
5) To make the coloring perfect, I also suggest you modify color in sprite image too , for your ease, I now include sprite’s image PSD too in included PSDs, if you dont find it you can download it here. https://www.dropbox.com/s/v8dkiw6yiyczsc4/Sprite%20PSD.zip
6) Go to Theme options and you will now see Red.css too in theme color options.
Select this red.css and Save theme options.
If you have any question feel free to contact me.