One of the first questions you have when mixing paint for application is whether it is compatible with other paints for modifying colors or other reasons.
For the most part products of the same paint type are mixable however you should always do testing before you rely on a paint for yourself or your customer and because it is so easy to shoot an email to a manufacturer you should probably contact them before you become a mad scientist.
In this case we are considering mixing a urethane base or single stage paint with a Urethane Clear.
The reason you might want to do this would be for tinting, applying over chrome or to convert a base coat paint to a single stage so only one application is necessary to get a glossy product in the finish.
Candy paints which are highly reduced with clear are painted over a silver base coat all the time but these products have gone through a lot of testing to get the formula right. Candy also doesn’t normally contain metallic flake but it can and even if you are applying a candy color you should follow up with a clear on top to protect it.
This may not be possible in every situation such as tinting chrome wheels where a thin coat of paint is often better so it will not chip under abuse.
The reason you have is up to you but the answer is Yes in most instances a Urethane Enamel Paint can be mixed with a Urethane Clear.
Some manufacturers will recommend that you activate the products separately and then mix them but this can be complex.
Your best bet is to use products from the same manufacturer and product line if compatibility is most important.