Wendy, the coloring of the stretch marks will fade over time.
As a GG I have had three kids and as Brooke can attest I have horrible stretch marks on my tummy, very wide etc. Mainly because I had 2 of the 3 pregnancies mainly back to back. They have faded to regular skin color (they just seem shinier).
WRT to products...there are several you can try that you can get right at your local drug store. I personally swear by vitamin E oil but not lose oil in a bottle. Buy the capules, pin prick them and squeeze the vitamin E oil out of them and rub into the skin all around your breast and anywhere else HRT is adding mass/curves (hips, butt etc).
Unfortunately once you have developed stretch marks you can't really take them away, but you can prevent more as well as minimize what has already begun.
As LynnER said Retin-A is great however over the years they have discovered many side affects so check on that before you go gung ho on it.