rgb leds

the longest pin of a an rgb led is the grd. i have to give power to 1 3 or 4 pin and grd on 2 to have light instead of this when i put grd on 1 3 or 4 and the power to 2 i have light when i use it with arduino ( i did not use it other way i do not have the means to do it)
can anyone help me about this?
thank you in advance

You can get common anode or common cathode RGB LED's. Maybe you have common anode and not common cathode (as fits your description). Common cathode have a common ground pin and 3x power pins for R,G & B. Common anode has a common power pin and 3x pins to ground the R, G or B.

you saved me i tortured myself two days now trying to understand what's up thank you