What Causes Skin Pigmentation While Having Adrenal Insufficiency?

My 3 year old daughter has been diagnosed with an adrenaline deficiency. She already has skin pigmentation which has made her skin quite dark and yellowish in colour. Dr has not given any meds for this only done a urine test and said her kidneys are not affected. We have to wait and see. Is this normal and will the pigmentation lighten over time?