Why is red hair called "руде" instead of "червоне"? Is there an interesting history behind it?
I don't think there is a story behind it (although you never know), it's similar to how you don't say that somebody's hair is light-yellow or white in English, you'd say they are blonde.
Or in French they have rouge for red, but roux for red hair (or for a ginger).
The question should be the other way around: why "red hair" is called "red" and not "orange" in English :) There's a nice story about it from the times where people didn't have many words for different colours (e.g. for purple and orange, and way back in the past even for yellow).
Рудий is the name of just... that colour. Other things that can be рудий are, for example, leaves, rust and bricks.