There’s no way to make the total a different color if it is zero, nor to make it blank if it is zero. Even if you could do this, however, you still have the problem that 8.50 hours looks a lot like 0.50 hours.
If your employees never report negative hours, then you should be able to hide the zero totals by using the selection formula to exclude from the view any documents that don’t report any hours.
Or, generate your own report on the fly using a rich text field, then you could format everything however you like.
I have to tell you, though, I have no trouble distinguishing an 8 from a 0 in any normal font, provided they’re displayed big enough to see…