I would suggest that you go to see your primary care doctor
about this issue. There are a few different things that could be causing the change in the color of your fingernails, some of them serious and others not. Your doctor will be able to perform an examination and help you figure out whether or not this is something that needs to be looked at more closely.
For example, a fungal infection of the nails may cause a range of different color changes, as well as thickening and distortion of the nails. Although this would be unlikely to affect all of your nails at once, it could be going on if the changes are just in a few nails.
Low blood oxygen levels can cause the nail beds to be bluish in color. This is a problem that is common in those with advanced lung or heart disease.
Undiagnosed diabetes may also produce changes in the nails, including thickening and a bluish discoloration at the base.
Finally, excessive use of nail polish and nail polish removers may cause changes in the color and texture of the nails.
Start by making an appointment with your primary care doctor at your earliest convenience.