Weights and Scale: a variation.

You have 6 weights which appears almost identical but 3 of them are slightly heavier than the remaining 3. The 6 weigth have 3 colours: red, green and blue. For each colour there is a pair of weights and one of the weight in the pair is slighlty heavier than the other. How many times do you need to use a scale with two plates for identifying the lighter weights?