Probably have to know more about your 'bar of rgb led's and how they are wired up. A drawing showing the individual leds and how they are wired to each other would be a good starting point. And on using a pot to adjust current flow, I would propose that you are best off using both a resistor and a pot in series such that turning the pot to 'zero ohms' position doesn't burn everything up. Calculate the fixed resistor to set the absolute maximum current flow and then allow the pot to dim from there.
Lefty