Curious as to why are my teeth roots going brown very fast?

Roots are. Generally more yellow or brown in color compared to the clinical crown (tooth portion). The texture of the root is also not smooth like enamel and can stain easily - coffee, tobacco etc. Best to check with your dentist however. Hope this helps.
Hard to say... Could be decay, could be staining. A consultation with your local dentist will get you a definitive answer and the appropriate care.