A red banana is a banana with a distinctive red to purple skin, rather than the more conventional yellow. These bananas originate in Costa Rica, where they are extremely popular, and they are widely eaten in other parts of Central America. The skin of a red banana may be anywhere from dark red to almost purple, and the flesh is cream to slightly pink in color.
On a traffic light green means ‘go’ and yellow means ‘yield’, but on a banana it’s just the opposite. Green means ‘hold on,’ yellow means ‘go ahead,’ and red means, ‘where the hell did you get that banana at?’
— Mitch Hedberg