Yellow nail syndrome

It is a very rare medical syndrome, otherwise known as “primary lymphedema associated with yellow nails and pleural effusions”.
The nails are visibly thickened with yellow discoloration and tend to grow more slowly than normal. 

Most people with yellow nail syndrome also have lymphedema, due to the underdevelopment of the lymphatic vessels, a symptom that is associated with this syndrome.
Yellow nail syndrome has been associated with some anti-rheumatic drugs, as well as with exposure to titanium from dental implants or consuming food containing titanium dioxide.