But black also radiates the heat away quicker. The actual difference to the person wearing a black or white T-Shirt has been shown to be negligible.
Other points for black include:
Won't turn pink when you put it in the wash with a red item of clothing by mistake
Doesn't show the grime picked up from cleaning/repairing a machine meaning that you can wear the same shirt all weekend and just keep spraying it with deodorant (if the rest of us are lucky) in the forlorn attempt to mask the BO.