Mine turn white when my weight is stable, and turn red when I lose or gain large amounts of weight. They were white after I had been consistently at 230 and then, after my 30lb gain, they have gone red again.
I believe once your weight stabilizes they start to become less red/purple and more white, but I could be wrong. That's just what happens to me.
The ones on my breasts are white, probably because that area of my body is the last to change during weight loss/gain.
Stretch marks are funny things, but I find I don't care what they do anymore. When I lose the weight they'll just be a reminder of the great thing I did, and if I want to wear shorts I'll work something out. I personally don't care for shorts anyways, so maybe I am biased, though I do have stretch marks on my arms that are white and they are fairly obvious in the sun, and I like to wear shorter sleeves. I'm more concerned about getting rid of the flabby fat the hangs out there though.
Stretch marks are like pimples to me. There's not much you can do about them except hope they become less visible with time.
Maybe not the answer you wanted, but most women have stretch marks, especially on the stomach, and I think people should give them less attention.