The bizarre hair colors seen in modern anime have their origins in the black-and-white manga source material. In a nation where virtually everyone has black hair, characters in manga (who often had very similar facial features as well) could be difficult to distinguish from one another. One solution was to give them different hairstyles or to use variant shading (or no shading at all) on their hair. When the mangas were translated to color animation, the odd shadings were sometimes translated as bright colors. This trope/concept particularly exploded, however, with the advent of computer video games in the 1980s - due to palette restrictions, giving characters "natural" hair colors, black especially, that read well on-screen was often enormously difficult. Bright hair colors in the red, blue, purple, and green ranges, however, often translated very well to the screen and often made it easier to track characters visually on screen. And given the cross-promotion and cross-inspiration between anime and video games, even in the 80s, the concept transferred very quickly.
In most cases, these unnatural colors are understood to be normal, natural shades by the other characters. That is to say, the color carries none of the social connotations it would in the real world, and other characters rarely if ever react to it as unusual in any way. This may indicate that the color used is more a visual shortcut than a real color - e.g., perhaps the cast of Ranma does in fact have black hair, but, just as their eyes are drawn nothing like real eyes, their hair gets drawn nothing like their "real" hair. Dark blue hair, in particular, is often understood to be a "stylized" black, used in instances where actual black hair simply would not read well visually.Ranma's girl-form is a redhead, the manga version has black hair and is able to masquerade as a regular Japanese girl without a wig or hair dye (though Takahashi played with this and drew her with different-colored hair on the times when it was colored, but used red more frequently later on). Similarly, Shampoo from the same series has bright purple hair in the anime, whereas in the manga, it was limited to subtle purple highlights |