The pumpkin was not used because it is native to the Americas, and by the time man came to the Americas, he had already acquired a word for orange during his passage through Eurasia.

As for the persimmon, that's more of a mystery, because it is also native to Southeast Asia, but I had never heard of persimmons in my life until you mentioned them today, which makes me think it's probably less widely distributed, and that thus humans may not have encountered them until after they had encountered oranges. There are other reasons possible here, too: 

* The persimmon's color is not quite as distinct as the orange's; it's closer to red than the orange's (meaning the citrus').

* The persimmon appears to rot faster than the orange, making it harder for it to spread through commerce.

And yes, surely the fruit inspired the color name.

You should also have asked about the carrot. The wild carrot originates in Europe and Southwestern Asia, which was in the path of humans migrating out of Africa earlier than Southeast Asia was. But the wild carrot was a) buried under ground, not really prominent until it became domesticated, and b) not really orange in the wild form as far as I can tell --at least not bright orange, and not consisntely orange.

Indeed, the modern carrot appears to have been introduced to Europe in the 8-10th centuries;[citation needed]. Ibn al-Awam, in Andalusia, describes both red and yellow carrots; Simeon Seth also mentions both colours in the 11th century. Orange-coloured carrots appeared in the Netherlands in the 17th century.[http://en.wikipedia.org/wiki/Carrot:8]