In German, we also call that colour of hair "rot" which translates as "red" into English. I agree that "red" hair is not red in the same way as most other "red" things are, but I still use the word when I'm talking to people from other regions in Germany. When I'm talking to people from my own region, though, I prefer the term "fussig" which is from the local dialect and means the same.
I reckon the reason for this linguistic inconsistency is that "red" hair has been known in Europe for a very long time and Red was the colour that came closest to it inappeareance. The term "orange" was not known in Europe at all until about the Middle Ages, when oranges (the fruit) began to be imported from China. The word first described the fruit and only later was adopted for its colour. Thus quite a number of things were originally described as being red that we would consider orange nowwaddays.
Another example is the European Robin whose name in many European languages bears connection to the colour "Red" it displays at the throat. In German, we call these birds "Rotkehlchen", which means "little red-throat", even though their throat and breast are much closer to Orange as can be seen in this pic.
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Yes, I am serious about that avatar...