How to make something keep going until it reaches to a certain thing?

The title says it all, how do you make something keep going until it reaches to a certain thing, so like if I keep pressing a button and the part keeps changing colors it stops changing colors when it becomes yellow or green idk, I've tried looking at loops and stuff but I don't really know if that option works.

Hey man, seems like you talking about loops? For something like your example you would want to do something like:

local button = gui.button
local part = workspace.part

-- Wait for mouse click
button.MouseButton1Click:connect(function()
	-- loop the code but break the loop once it has gone red
	while part.BrickColor ~= BrickColor.new("Bright red") do
		-- if its not red run this code
		part.BrickColor = BrickColor.random()
		-- in loops always remember to put a wait otherwise the game will freeze
		wait(1)
	end
	-- if the color turns red then the loop will stop yielding and the rest of the code will run
	print('The brick is now red')
end)

This was more giving code than an explanation, so for mroe advanced stuff read mroe about loops here: http://wiki.roblox.com/index.php?title=Loops