thanks for playing! there is no set color that a plus can recolor you to. you switch between red-orange-yellow-green-cyan-purple, so there's no way to color the pluses because what color it gives is based on the order you take the pluses if there are multiple
there are, in fact, colored pluses in the game that set your color to their own, but i haven't got to use them in a level yet, partly because i was running out of time
just looked into arrow controls - i've just accidentally assigned "down" to moving up haha, this will be fixed in the nearest update