My teeth are clear/greyish looking instead of opaque white. How do I correct this

Dental bonding can definitely mask the clear or grey color on your tooth if applied from outside surface!If you desire the dental bond to go from inside, that all depends on your bite, it needs to be evaluated! Understand that it may fracture! Ask your expert dentist to do a mock up first, and then evaluate!Best of luck

The presence of translucent enamel on the incisal edges is natural- often times laboratory technicians try to mimic this to a certain degree when making aesthetic porcelain restorations. 
That being said, if you think they are too gray then there are different options. If the teeth are too thin due to wear on the back surface, then it is possible to try bonding to make them less translucent. However, if these teeth touch your lower teeth when you bite down, then the bonding here may be in the way and affect the bite- in which case it is probably not advised. If this were the case, bonding on the facial surface, or veneers (prepped or prepless) may be the only other option. I would suggest an evaluation with your dentist to review options based on the history of this translucency and positioning / bite of the front teeth. 
Hope this helps!