You should consult the qualified doctor for the exact cause.
But if is caused by fungus infection which you can also see and decide by the help of following symptons given.
Toenails get flaky
Toenails get brittle
Toenails keep getting chipped
Toenails get a yellow, black, or brown tinge or spots
Toenails get thick and pain while wearing shoes
A bad smell emanates under the toenails
While walking, the skin under your toenails feel a stinging pain due to the fungal infection.

If this is the case, then do the following home remedies to eliminate the fungus.
1. Vinegar
Fill a basin with warm water and vinegar in equal proportion (any vinegar will do, but apple cider vinegar has proven more effective). Soak toenails in this solution for about 20 minutes. Wipe the toes and toenails thoroughly with a dry towel and then with super absorbent paper.
2.Tea Tree Oil
The uses of tea tree oil are many. Tea tree oil is a natural and powerful fungicide and antiseptic. Rub the affected toenail/s with a cotton ball dipped in tea tree oil. Do this twice daily, morning and just before going to bed (three times if possible) for maximum effect, until the fungus is gone.
3.Listerine
Almost all homes will have this mouthwash. Soak the affected toenail/s in Listerine for about 20 minutes twice daily. The antiseptic will help eradicate the fungus.

Try and avoid those bathrooms where the fungus thrive and you can be infected by the fungus left behind by someone else. Never use nail clippers belonging to someone else for the same reason.

You should consult with your child Physician because race in not an issue, but for some
black African American's, skin around their fingernails and toe nails get darker a s a result of simple reasons such as the sun. Strong chemicals can cause this discoloration, too, resulting from the irritation.

Nevertheless, discoloration of the sking around the fingernail does not appear to be of any significant evidence of a major disease. If there are any other symptom appear e.g. Lesions around nails, you should see a doctor right away, they could be indication of a Thyroid abnormality.

Hope this answers your question!

REFERENCE(S)

1. Riverside Health System. (2007) http://www.riverside-online.com/health_reference/Tools/WO00055.cfm

2. DermNet. (2007) http://www.dermnetnz.org/hair-nails-sweat/nails.html#cuticle

3. DermNet. (2007) http://www.dermnetnz.org/hair-nails-sweat/nails.html#cuticle

http://www.dermnetnz.org/hair-nails-sweat/nails.html#discolo ured

A person that won't TREAT you right, damn sure won't TEACH you right!