Well here's the tricky thing about LEDs and turning your bud purple in my opinion.
LED usually pump out a heavy purple spectrum. This would be ideal if you wanted your plants to grow any other color but purple. The way a plant's color, and any object's color in general works, is that the color that you see is the only color that the object does not absorb. This being said, most of the lumen concentration in a light with a purple hue is purple (since it is not bouncing off of any object you are seeing the color that the light is). Since you would want your plant to be purple, you are depriving your plant of a considerable amount of the lumens that your light produces.
Again, this is only my opinion, I could be totally wrong. This would just be something to look out for.
That being said. Getting purple is relatively easy, it's all about a cold climate. I've heard of people using ice water for the last weeks/flush period. Only times that I ever ended up with purple was because my night time temps were pretty low (usually during winter and spring harvest). Purple typically does sell for more, but be careful, if you fuck with your temps too much you can and will get brown buds. And no one wants brown buds.