2 weeks post op hair transplant; can i colour my hair which is non transplanted (original)?

If your doctor said you should wait 3 to 4 weeks after hair transplant, it would be best to follow that advice.

I don't think there is any data to give you any clear guidance on when you can color your hair following a hair transplant.  In performing FUE on individuals with white hair, we often dye the hair we have shaved to 1 mm length just prior to the procedure. While allergic reactions to the dye are possible, we have never seen one.  We also have never seen this negatively impact the procedure.  In theory, once the wounds are healed, dye cannot penetrate a closed wound.  If you have never had a reaction to the dye you typically use in the past, you should be able to safely resume dyeing upon skin healing.  I think all of the recommendations here have some degree of merit, but remember that this has never been studied so there is no objective data to support any advice on this matter.  

Would recommend waiting at least 28 days for all wounds to heal and then using only an organic tint product such as Herbatint.