How to tell a common cathode vs a common anode full color led?
If you can see the internal structure you can tell from whether the dies are on a common leadframe or whether the wire bonds go to a common leadframe (possibly it will be 2 of 3).

As to which is which (which you didn't ask), I don't keep that in my skull but it's easy enough to figure out. 

Failing that, a battery, resistor and a couple jumper wires will allow you to 'visually' see which way the LEDs swing.