Click the colorset tab when starting a game and select it
That only is there if you have an
RTB (Return-To-Blockland) account.
There are other ways to use a custom colorset. Here's one:
Open your Add-Ons folder.
Find your custom colorset, and locate the default colorset.
Open your custom colorset folder, and find the- colorSet.txt
Take that file out, and replace it with the one in the Default colorset.
Hope this helps.
-daniel_bc (AWESOME :D)