Hi, good questions.
I'll assume that you do not have all the decks yet. I did not bother to check the order, but There are bunnies that come out that are half-color bunnies. Two examples are:
Yellow/Blue Gleeful Bunny (332; Run) May be used to form Bunny
Triplets (three matching bunnies) as either a Yellow or a Blue Gleeful
Yellow/Green Congenial Bunny (331; Run) May be used to form
Bunny Triplets (three matching bunnies) as either a Yellow or a Green
So therefore rainbow would kill both these bunnies if yellow were chosen. And would kill the yellow/green bunny but not the yellow/blue bunny if green were chosen. (even though yellow and blue make green, but that's in art class not Killer Bunnies)
As to the barriers (always remember that the bunny circle is to be viewed as a continuous circle.) Imagine that the barriers in the example you gave would divide the circle into two parts as follows :
Barrier; Player A's bunnies; Barrier; Player B's Bunnies; Player C's Bunnies.
In this case many cards would only be able to affect either play A OR players B and C. In the case of Rainbo; if it were played on player A - only his bunnies would be affected. But if Rainbo were played on Player B Or C then Player A's bunnies would be safe. As to a roaming red card: It depends on where the roaming red card is started Cyber Bunny
may be played on any bunny which must roll higher than ‘09’ to survive. would similarly attack only the bunnies in the same area (defined by barriers) that he was placed. In other words; if he were placed in player A's area, he would only attack A's bunnies; if he were placed in player B's area or player C's area he would attack only their bunnies. In either case once there were no viable targets inside the section of the bunny circle he was in the cyber bunny would be discarded.
The use of barriers is a two-edged sword. You can isolate a player using barriers, but that could be used against you as well as for you. One example of an effective use of barriers would the cyber bunny example above. This could wipe out a players bunnies. BUT if he had another bunny available, or one that survived. He could then launch a weapon, such as the Miniature Black Hole that could possibly wipe out all the bunnies of both players B and C.