Usually the colour of the bud can determine its potency, brown pot usually sucks -rego (25 a quarter) Green bud with red hairs-mids (50 a quarter) and then you have lime green bud covered in a white residue, white hairs and usually has crystals- Chronic (100 a quarter) Then you have REALLY good chronic like Northern Lights, and the famous Purple Haze. (110 a quarter) Real purple haze is completely purple with white hairs all over it and crystals everywhere. So if you have good chronic and part of the bud is purple, you know its some good stuff.
Funny story, I've only gotten real purple haze once in my life, and I went with my friend and smoked with a couple other people like 3-4 bowls. I was so high my body went numb and I was just like a vegetable... it felt so good and it was a really clean high. I wanted to buy a gram off of him but I didn't have the money on me, so I asked if I could pay him through paypal, and he let me! :P I even put 1g Purple Haze as the reason for the sent money.