Rainbow can be broken by any Icebreaker in the game except for Mimic, Yog.0, D4v1d (technically not an icebreaker) or Grappling Hook (also technically not an icebreaker).
Mimic and Yog.0 can easily get through Rainbow with the help of their friends Datasucker and Net-Ready Eyes.
I suppose Gingerbread, Deus X and Sharpshooter also count but they will often be accompanised by Panchatantra.
Quetzal: Free Spirit can walk right through (once per turn). Depending on the positioning Rielle "Kit" Peddler: Transhuman might be quite happy too.
With a weaknesses like this Rainbow would need some major upsides or strengths to warrant inclusion in anyone's deck.
- 3 to rez for a Str 4 'hard' End the run.
- As the outmost piece of Ice on a server it will 'take the bullet' from Forked, Knifed or Spooned, protecting your better ice from destruction.
- Str 4 also means it either takes 3/4 turns or a number of Datasucker counters to trash with Parasite.
- Against decks using an AI breaker like Eater or Faust it is no weaker than a Bastion.
- Zero influence.
So we can say that Rainbow is kind of 'strong' against Ice Destruction and okay against AI breakers. But if you don't like Ice destruction you've got Architect and Lotus Field. If you don't like AI breakers you could use Swordsman, Turing or Wraparound.
Does it combo with anything?
- Superior Cyberwalls counts it as a barrier
- Encrypted Portals counts it as a code gate
- Unorthodox Predictions makes it unbreakable for a turn
Not an impressive selection in terms of combos either.
The only circumstances where Rainbow will outperform other ice is if your local meta is full of Anarchists who use AI breakers and ice destruction but don't have a lot of Mimic/Yog.0/Datasucker. If this is the case, go ahead and make them taste the Rainbow. Otherwise it's hard to have much pride in this piece of Ice.