Redness from pimples that a LONG LONG time to go away, a year minimum if its a dark red initially. I still have a very slight pink blemish from a super-pimple 13 months ago.
The good thing is with HRT, I don't get pimples anymore YAY!!
You could use tretinoin (retin-A, renova, etc) to accelerate skin turnover and repair the deeper derm layers; by accelerating skin turnover, it will fade faster.
Also, I heard that doing several glycolic peels can make them go away faster. But, I prefer using tretinoin. Its very good for skin tone in general.