What is the cause of colours of nail
The Nightman is giving you a headstart to understand and read about nail colour. 

I would like to add a different view to this question from "Colour and Pathology" point of view. Finger nails have been an excellent source of evidence for the initial physical diagnosis process. Nail colour and texture can be an indiator for a wide range of medical conditions.

You may take a look at this link : The hand in Diagnosis Process and discusses about nail pathology.. However this diagnosis gets a little tedious if the patient has colourfully painted their nails with nail polish...

I see many of the answers do include an image - well at the end it's anatomy.



Here's a relative simple and fun to read article to clarify any doubts you have about Keratin in nails being dead or not, for its colour and why it's tough.


  The cuticle and matrix are white because the melanocytes there are inactive, so there is no pigment produced. The matrix cells divide and the new cells produce a lot of keratin protein. 
  
  The older cells fill with keratin and die, and the new cells push them out of the way – this means toward the end of your finger. This is how your nails grow.
  
  But our fingernail doesn’t look like individual cells. You are
   sloughing millions of skin cells each day, but for a nail the dead
   cells all mass together. Nails only wear away or must be trimmed.
   Individual cells are not lost. The solidity of the nail comes from the
   connecting of the dead cells together by junctions between the cells
   called desmosomes, and by the interlocking of the cells like jigsaw
   puzzle pieces. But there’s more.
  
  Individual keratin protein filaments also become connected so that the entire mass of keratin becomes one solid structure. This is called cornification, like the stratum corneum (the outer, dead layers) of your skin.
  
  One of the two main forms of keratin in your nails is crystalline keratin, which is rigid, stronger, and has an ordered structure - like a tinker toy cube. Transmitted light is less likely to strike an atom and bounce back when the atoms are all lined up, so this is why many crystalline lattices appear translucent.