For people with mild to moderate PPD allergies, direct dyes are sometimes a life saver. These are the kind of dyes that are one step, no mixing. Of course, they have very different diamines in them as well. At Sally's, you can use Manic Panic, or Jazzing, or for a professional route, you can try Goldwell's Elumen or J Beverly Hills just released Fashion Colors. The dark natural colors in these brands are not all that great. They are all temporary colors, or semi-permanent at best. The best for natural colors is Cosamo. I haven't used it yet, but it seems promising from the client reviews. The customer service is great too.
I can not stress enough that you will want to do the 3 step patch testing that I have covered previously. If you have severe allergies, this is not for you. The red manic panic has had a few reactions as well, so patch test!
Remember, this is NOT a proven color for PPD sufferers. Please use extreme caution. If you react, call 911. Do not use this alone, so if your airway is constricted, someone else can speak to 911 for you. If you start to go into an allergic reaction that is severe, don't drive to the doctor, or the emergency room. The time it takes for your airway to swell is extremely short, so safety is a must.
Best wishes, with caution!