'Fair' can mean any light-colored hair - blond or light brown (sometimes called 'dirty blonde'). 'Blond' refers to straw-colored (yellow or lighter) hair color. 'Fair' also refers to light-colored skin, whereas 'blond' only refers to hair. 'Fair' can also mean pleasing to look at, though it is used more in older English. I have read in some research that long ago, 'fair' used to refer to a woman that had no smallpox scars, back when smallpox was a major disease. The usage has obviously changed over the years.

'Hair' is much more common than 'hairs'. Hairs is typically only used when talking about a few stands of hair. For example, "I found a few of my hairs caught in my comb" versus "I use my comb to arrange my hair". With your gray hair example, I wouldn't call grey hair "fair". Fair hair is typically used to describe a range of hair colors from a light shade of brown to pale yellow. A blonde is usually someone with yellow hair. So you could say all blondes have fair hair, but not all people with fair hair are blondes. I hope that helps.

Hi. :) We say "hairs" if we are counting them, ie. perhaps there are only a few hairs. "Hair" (ie. the hair on your head) is treated as an uncountable noun because it's simply too difficult to count every single unit!

Thanks fdmaxey. So can we say for example if someone has gray hair (light black) he/she has fair hair? And when do we say "hair" and when "hairs"?