When I heard my son calling his friend "Ginger" the other day, I had to ask why. I was surprised to hear that it is a nickname for redheads (I was surprised because my mom is a redhead and in my 40 plus years I have never heard of redheads being called "Ginger"). When I probed further, I was told that it came from an episode of
South Park with a group of redheaded children. Now it was starting to make sense to me. I had never heard the term because I do not watch
South Park. But then I started to think more about the word "ginger" and about redheads, and I remembered
Gilligan's Island. The character Ginger on
Gilligan's Island was a redhead so maybe the redhead/ginger connection goes back further than I first thought.

According to the pertinent entries for the
ginger in the Oxford English Dictionary (shown below) , the redhead/ginger connection dates as far back as 1785.
4. dial. and slang. a. A light sandy colour, resembling that of ginger.
1865 DICKENS Mut. Fr. I. ii, Mature young gentleman; with..too much ginger in his whiskers. 1889 N.W. Linc. Gloss. (ed. 2), Ginger, a light red or yellow colour, applied to the hair.
b. A cock with reddish plumage; also, a red-haired or sandy-haired person.
1785 GROSE Dict. Vulg. Tongue s.v. Ginger-pated, Red cocks are called gingers. 1797 Sporting Mag. IX. 338 In cocking, I suppose you will not find a better breed of gingers. 1857 H. AINSWORTH Spendthrift xvi. 109 Examining the cocks, and betting with each other..this backing a grey, that a ginger. 1885 in Eng. Illustr. Mag. June 605 There is..‘Ginger’, the red-haired, who [etc.].
But why ginger for a red-haired?...to me ginger is white.

I can't answer that question, but I did find the following dialogue on
Explain the Ginger.
oneirodynia, actually Curcuma amada (mango ginger) is different from turmeric (Curcuma longa. It's a variant of ginger with a distinct mango-like taste. It's actually very tasty made into a pickle. It's quite common in India.posted by peacheater at 7:03 PM on February 8, 2008 Yes, but the point is that Curcumins look like ginger, and most if not all have orange/red dying properties, and some of them were known in England as "ginger" in spite of not necessarily being what we call ginger today. Curcuma are in the Zingerberaceae family. I'm not trying to say tumeric and mango ginger are the same thing.posted by oneirodynia at 7:52 PM on February 8, 2008 On the other hand, maybe the term ginger is used to refer to a redheads because the flower of the ginger plant is red.

P.S. Apparently in Australia the nickname for a redhead is "bluey" because of the Australians' appreciation of irony. Though I did read somewhere (I can not remember for the life of me where), that it could also have to do with vegetable colors, specifically the Australian blue squash which has teal-gray skin encasing bright orange flesh.