achromasia

from The Century Dictionary.

• noun In pathology, lack of pigment in the skin.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Absence of normal skin pigmentation (from bruising, stress or disease); pallor or achromia
• noun The inability of a cell or tissue to be stained

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun unnatural lack of color in the skin (as from bruising or sickness or emotional distress)