Hey there,

That's Post Inflammatory Erythema - it fades with time. To fasten the process you can use Tretinoin (pea sized) - need a prescription to get this.
But, even with Tretinoin - its a process - doesn't disappear over night and can take up to or more than 6 months. But hang in there, because they're not permanent and eventually WILL fade.
Just a matter of time.

Cheers,

do a forum search on how to lighten post acne marks.