It is worth noting that the colours pink and blue have only been ‘traditional’ for girls and boys in Western countries since the 1930s-50s. A popular American women’s magazine (USA) called Ladies' Home Journal reported in a June 1918 article that, "The generally accepted rule is pink for the boys, and blue for the girls. The reason is that pink, being a more decided and stronger color, is more suitable for the boy, while blue, which is more delicate and dainty, is prettier for the girl." Major clothing stores in US cities also advised parents to buy pink clothing for boys (quoted in Pink and Blue: Telling the Girls From the Boys in America, by Jo B. Paoletti, 2013, Bloomington: Indiana University Press).
The appropriate colour for a gender to wear is changeable and culturally determined, like gender roles themselves.
Like the colours pink and blue for trans people, the colour purple has been adopted by many bisexuals as a marker of identity. The bisexual pride flag, with pink, purple and blue stripes, was designed in 1990 by Michael Page to increase bisexual visibility. "The pink color represents sexual attraction to the same sex only (gay and lesbian). The blue represents sexual attraction to the opposite sex only (straight) and the resultant overlap color purple represents sexual attraction to both (bi)…. The key to understanding the symbolism of the Bisexual pride flag is to know that the purple pixels of color blend unnoticeably into both the pink and blue, just as in the 'real world,' where bi people blend unnoticeably into both the gay/lesbian and straight communities" (click here).
A variety of garments and accessories such as footwear, hats and jewellery have been produced in these different colours to express different identities.
A different sort of flag also involves colours. Flagging, also called the hanky code, involves wearing a coloured handkerchief (or neck bandana, or, more recently, fingernail polish) to signal what specific sex act the wearer wants. The handkerchief (the colours range from different shades of red to pink, blue or green to yellow) is worn in the left pocket or the right. The side indicates whether the wearer wants to be passive or active during sex. Flagging was popular in gay bars and cruising areas in the 1970s, when homosexuality was criminalized and discretion was necessary in order to avoid police arrest or harassment. Flagging’s origin is uncertain, though some historians think it dates to at least the late 1840s or mid-1850s. There are reports that heterosexuals have adopted the practice of flagging.