So why don’t we say “orangehead”? Etymology to the rescue!
The word “red” in English dates straight back to Proto-Indo-European, via Proto-Germanic. This is consistent with what we know about colour terms cross-linguistically: after black and white, “red” is generally the next earliest colour term that a language is likely to have.
“Orange”, on the other hand, only appears in English after the arrival of the fruits in England. The term for the fruit shows up around 1300 A.D, and doesn’t start being used for the colour until the 1540s.
What about “redhead”? It started being said in the mid-1200s, about a hundred years before English speakers were even talking about oranges, let alone the colour.
We don’t say orangehead because when the term was coined, English didn’t differentiate between “red” and “orange”. (Kind of like the way today we don’t have different terms for light blue and dark blue, even though other languages like Russian do have separate words for these.)
So the next question is, why did it take until the arrival of oranges in England for people to have a handy orange object to name the colour after? Surely they could have named this colour “pumpkin” or “carrot” instead, right?
Pumpkins were first grown in North America, which means that Europeans had never heard of them until there started to be lots of contact between these two continents. So that’s 1492 at the very earliest, but Columbus was mostly between the Caribbean and Spain, so the word “pumpkin” doesn’t show up in English until the 1640s (from the 1540s “pumpion” was used for melons and pumpkins, but these come in several colours so probably not good sources for unambiguous colour terms).
This also explains why “melon” wasn’t chosen, since there are several colours of melon. “Cantaloupe” isn’t used in English until 1739…much too late.
What about “carrot”? This word is pretty old, coming into English in the 1530s. But there are two problems: firstly, “orange” as a food had been around for about 200 years already, and second, carrots originally looked like this:
Not very orange, huh. Carrots were also available in red and yellow, and the orange carrot wasn’t very common until the Dutch started cultivating them in the 1600s. Rumour has it that this was in honour of William of Orange, but at any rate, when people started saying “orange” for the colour in the 1540s, carrots were still this weird purple vegetable and pumpkins and melons were still the same category of food. So “orange” seemed like the best option.
However, there’s another old food term that managed to do quite well for itself as a pretty illogical hair colour name.
Ginger is goldy-yellow! Why aren’t we using this to mean “blonde”? There are some questions that even etymology cannot answer.