Etymonline shows
orange
c.1300, from O.Fr. orenge (12c.), from M.L. pomum de orenge, from It. arancia, originally narancia (Venetian naranza), alteration of Arabic naranj, from Pers. narang, from Skt. naranga-s "orange tree," of uncertain origin. Loss of initial n- probably due to confusion with definite article (e.g. une narange, una narancia), but perhaps influenced by Fr. or "gold."
…
Not used as the name of a color until 1540s.
I am really interested in more details on why 'orange' (fruit) was chosen to represent the color. Also, if there are sources that systematically deal with names of colors in different languages or changes over time that would be very interesting, too. Colors are an example of a very stable (static) concept with corresponding terms ('main' colors) for which throughout history there had been a need (more or less important) to have words for.
Bonus question is — what was orange called before 1540s in English?
Best Answer
To support the explanation offered by Philoto invoking the intuitiveness of deriving the colour name from the fruit name one can only notice that the phenomenon is a widespread one, observed in many languages and suffering only a few notable albeit easily understandable exceptions.
Here is a whirlwind tour of the various family of names for the fruit and its distinctive colour.
Exceptions
One notable exception is the common case of many northern countries in which the fruit has two concurrent names. an older one taken from Old Dutch appelsien 3 now sinaasappel and a newer one taken from English orange. In which case the colour itself is most of the time a cognate of orange.
In Dominican Republic, the orange colour is actually called "mamey" after the local fruit named Mammee. One has to mention though that they do have oranges over there but these are actually green. The Mammey instead is... orange. QED.
Note 1
German Wikipedia
Während die Bitterorange spätestens im 11. Jahrhundert nach Italien gekommen ist, wurde die süße Variante erst im 15. Jahrhundert nach Europa eingeführt, wo sie zunächst fast ausschließlich in Portugal angebaut wurde.
Translation: Although the bitter variety was already known inItaly in the 1th Century, the sweet variety was not introduced into Europe until the 15th Century, where it was grown almost exclusively in Portugal.
Note 2
Napolitan people will tell you that it comes from French "Pour toi" but that's folk etymology
Note 3
appelsien = Chinese Apple. There is no relation with the original sin although many German contemporary oil paintings depict Adam and Eve together with the snake coiled inside an orange tree.