Ah, I see. That's intended, but I saw from the stream that someone else ran into that issue, so I'll take another look at it. As for the solution - from the raindrop below the orange heart, you can go to the right and take the upper drop, you can't get back to the left.
As for the six colors, it's because we noticed that there were arguments that Indigo didn't count as a color on the rainbow and ran with it.