For many centuries, it seems that the Netherlands and its people have been associated with “orange” (oraanj in Dutch, I believe). I think it was/is the main royal dynastic name – the House of Orange – and many Dutch seem to associate the color with their country.
I believe that “orange”, the fruit, the word, and (later) the color, come from China. (In French, English, and Dutch, the original “norange” (approx.) became “orange” through mishearing the indefinite article). Perhaps the orange made it to southern Europe in the Middle Ages or a bit earlier, I’m not sure.
My question is: How did the Dutch ever come to associate themselves with a fruit that cannot be grown there? (I guess you could ask the same about Ulster, Ireland, but I think that was somewhat later).
And, for the sake of completeness, the link between the Dutch royal family and Orange in the south of France is that their ancestors in the sixteenth century inherited the principality of Orange. The head of the family therefore used the title Prince of Orange until they got created Kings of the Netherlands in the nineteenth century. Since then it has been used as the title for the heir to the throne, currently Queen Beatrix’s eldest son.
And the link with Ireland is that the Prince of Orange in the late seventeenth century became King of England as William III and was remembered by later generations of Irish Protestants as the man who saved/entrenched English Protestant rule in Ireland.
In both cases, the connection with the colour and the fruit is just a coincidence, but was one that was too obvious for them not to become political symbols.