Can i wear a black undershirt under a white dress shirt?

No. I would advise against it, as a black or red tee shirt would be visible under (through) your shirt, just as a bold-coloured brassiere is visible through a light-coloured blouse.

Under a white shirt, I would recommend a white undershirt, your preference of style.

Why? Do you want the black tshirt to show as part of your look? Because it will be very visible. I say No unless that is the look you are going for.

Uh...a reference picture would be better since your describing a lot of things. From trying to form a picture of it in my head it sounds like a bit much. Over doing it.

only if you want it to show through - if you don't want it to show through use a white undershirt.

Yes. Black won't show under white. (At least that's how it works for bras :])

yea. but I prefer wearing red under white.

dont. youll see the black sleves on your arms and itll look weird

if its showing then NO! if its not showing than YES!

um.. yeah i guess that could work ;D

yeh no maybe