Pale or whitish nails may be a sign of iron deficiency, often seen in the chronically ill. Darkening on the outside of the nail might indicate kidney disease. Bluish discoloration called Cyanosis can indicate that hemoglobin, which carries oxygen in the blood, lacks sufficient oxygen. Lung, heart, or pulmonary disease can prevent adequate oxygen uptake and distribution. Yellow nails are usually reactions to chemicals or cigarette smoke.
Psoriasis is indicated when arthritis and skin scaling at the elbow accompany pitting.
A large spot under the nail is caused by the nail separating from the nail bed and may reflect a number of illnesses. But not all nail color changes reflect disease. Some whitening and thickening is normal with aging, beginning around age 20. Vertical lines called longitudinal ridges and tiny white spots are usually regarded as normal. Race is a factor as well.