Transmission fluid is sort of a red in color however if the transmission fluid is older or burnt it may be a darker black color.
Old dirty oil would be a black in color while the transmission fluid should be a red in color and the transmission fluid could either be coming from the front seal, rear seal or transmission pan gasket.
Look around and see where the transmission fluid is leaking and get the transmission fluid leak fixed as soon as possible as it can cause transmission damage if you lose the transmission fluid and it gets to low.
So have a mechanic fix the transmission leak which can require removing the transmission from the vehicle to get to the seals and replace them.
But if the transmission fluid leak is coming from the transmission pan then it can be fixed by just dropping the transmission pan and replacing the seal around the transmission fluid pan.