How do you make it so when says /newcolor they get a new ChatColor?

A simple way to do it is create your own chat system - which is not to hard. I have implemented something similar so here is an idea:

local player = script.Parent.Parent.Parent
functions = {["/new"] = function()
data = game:GetService("DataStoreService"):GetGlobalDataStore()
valid = {["blue"] = function(data) 
	data:SetAsync(player.Name..": chat_color", 	{26, 0, 132})
end}
-- As an example
end}

Then when updating you just get the player's color [not at hard], assign the RGB values then update your chat.