I don't think it's accurate to say that moisture-tainted NaH goes from sky-blue to white. The colour of neat NaH actually ranges from white to light gray. The same goes for KH. Since group 1 hydrides are extremely reactive, you'd be able to tell whether it's tainted by moisture. The evolution of H2 gas is a very clear indication of moisture present in your sample of NaH or KH. It's a violent fizzing so it cannot be missed. In the case of KH and explosion is likely to happen if you have moisture present. This is why NaH and KH are sold as slurries in hexane or anhydrous ether, or as suspensions in mineral oil. Both do a pretty good job in excluding air and moisture from the hydrides.

 @Paolo Suating

Thanks Paolo, I should check my KH whether it's grayish or not. 

When using NaH or KH, I usually use 1.1~1.5times the required amount, extra amount can be quenched in workup anyway