No, it would not be a natural way to say "all the taxis are white."
You're looking for:
1
2
3
4
5
As was mentioned above means "the entirety of the taxi(s)" which requires a very narrow, specific context, although keep in mind that examples 2 and 3 (2 more than 3, though) can also mean "the taxi is entirely white." Lacking grammatical number, Japanese requires extra information/context to clarify part/whole distinctions which are very easy to make in languages like English, which do have grammatical number.