Big fan of the just making it a Tap/Hold and adjust the balance for Helminth.
Alternatively a tap to activate the ability, hold to switch modes. Starting mode could be determined by Energy Color (warm/cold or bright/dark). And as a balancing option for Helminth remove the hold to switch mode. That way people who subsume it would have to commit to one type of buff (based on their energy color).
Also an Icon that shows you what buff you have would be nice addition for ppl with visual impairments / color blindness.
Something along those lines: