with no clear it should be a foggy look i believe, no matter the color it should be kinda a flat look, with no depth!
unless it was wet sanded in between and after each coat, then it would look like this, even doing this though, you should still be able to tell right away in most cases what has clear and what doesn't.
also you can scratch a small place out of the way, and if you scratch it (depending the color though) you can scratch it with a razor and if it has clear then you will have white/clear dust around the area that you scratched.
there are probably other ways, but those are the ways that i can think of right away, but it should be pretty apparent!