Which flavor ice cream do you want?

That's fine -- or "What kind of ice cream do you want?"

Thanks, Khoff.

In fact, I posted only half the question. Are these two sentences equally natural and synonymous?

What flavor ice cream do you want?
Which flavor ice cream do you want?

Tom

Or
Which flavor of ice cream do you want?

Mr. TomWhat flavor

Just name the flavor from among every flavor of ice cream you have ever heard of.

Mr. TomWhich flavor

Name one of the flavors on a list (implicit or explicit) of flavors being offered or being considered.

what identifies.
which selects.

CJ

CalifJimwhat identifies.which selects

To careful speakers. A lot of native speakers use 'what' in both cases.