It is possible with no difference in meaning. (just an empahasis on the adjective)
In English we always refer to hair in the singular--actually, it is a mass/uncountable noun like "information" "water" etc. Unless we are referring to a few individual hairs as in: "There are some hairs on your shirt."
In the last case you are referring in, the word is τρίχες. "Υπάρχουν τρίχες στο πουκάμισό σου", a literal translation. About the singular of the word, μαλλί, you can find some examples, it is right but not standard and formal, also means "wool". It can be used this singular, but it seems to me no romantic :) or poetic.