Many possibilities. There are many possible reason...Damage to the nerves (such as with diabetic neuropathy), a pinched nerve in the back (such as with sciatica and radiculopathy), blockages in the arteries (such as claudication in smokers), blockages in the veins (such as with edema or stasis from being overweight), etc. This is a common complaint that your doctor should be able to help you figure out.
Maybe nerve disorder. One of the causes is peripheral neuropathy or a disorder of the nerves in the toes/feet. However, there are several other causes for this symptom. Hence would recommend having this evaluated by your physician/neurologist as there are certain causes that are treatable. For further info, you may refer to : http://www.Cosozo.Com/article/peripheral-neuropathy-when-toe.
Expand. Any other symptoms? How old are you? Are you diabetic? Ties change colors with cold exposure? Arthritis?