These often occur from iron deficiency, circulation problems and other problems of the body's endocrine system.
Cigarettes, hair dyes and even tints sometimes discolor the nails.
Dry skin gets worse in winter and/or colder months, and so does the condition of some nails. Some get brittle, which is why you have to be careful about soaking them in water with chlorine, soap or detergents. Rubber gloves and warm gloves worn outside in cold weather can help.
Don't believe what you hear. You probably don't have a mineral or calcium deficiency. White spots usually develop because you've hit your nails against something.
Greenish nails are usually a result of a localized fungal infection. If you find greenish nails under your nail polish, consult your health-care provider, as there are treatments for this kind of fungal infection.
Ridges can appear either vertically or horizontally. Horizontal ridges called Beau's lines can result from severe stress. Some of these ridges are genetic--they're inherited--and get worse as you age. Vertical lines can indicate poor nutrition or iron deficiency.
Sometimes your nail looks as if it's going to literally lift off from the nail bed. It's scary and could be a sign of psoriasis, a skin disorder. Or it might be because your hands are spending too much time in water, detergents or soaps. If this is caused from having your hands in water too much, you might want to consider wearing rubber gloves when washing dishes or doing housework.