In my twenties my friends and I were into it, and without exception all of us who were white, or just light-skinned, were
never so much as asked a question about anything related to pot, by a police officer. I was pulled over once and my friend had just smoked in the car, and it
stank... cop didn't even blink.
Now at the time two of my friends were black, and one was Sikh, and they stopped smoking first out of all of us, because if they so much as smelled vaguely of pot, they'd get hassled. When we all get together now over dinner or drinks, we still go back to the old joke my Sikh friend came up with, "Being white is like a superpower in this country."
It's not that simple of course, and the factors which determine whether the police will bother you are also based on socioeconomic status, and if you have a criminal record or not. In terms of actually catching the eye of the police though, my white friends and I just never did, while any of my friends who couldn't have passed the infamous "paper bag test" always seemed to have to explain themselves a lot more.
Note: NorthEast US, I cannot speak for the rest of it.
Sidenote: My Sikh friend normally has a decent time of it, but after 9/11? He and his family who had moved to Georgia, ended up moving back East.