I heard that there was an add-on for colorsets but I've looked it up and no such thing has appeared.
The only add-on you need is Blockland Glass, my friend. Blockland Glass doesn't have a color set section in custom game mode, unlike Return To Blockland which you are used to. In order to swap out color sets, you first need to hold CTRL and SPACE to go to the BLG home. Next, you select Mod Manager and add-ons. Once there, you select color sets and choose which ever color set you have installed.