Shoot it over whatever base color you want since it's clear. As to how much to mix in, that is up to you. The clear will only take so much, so there is an upper limit. The practical limit is much lower, I'm sure. Really going to be a matter of personal taste. Mix up a small amount with however much powder in it you think you need and do a test. If it's acceptable, proceed. If it's too much, add more clear. Too little, add powder. Jut be sure to weigh/measure how much of everything so you have somewhat repeatable results.

Keep in mind that once you get it the way you want, you better have enough to do the current plane PLUS any repairs, and then some, so that it will match. You're making a custom color/top coat, and the chances of later mixing up a batch to match perfectly is fairly slim. If you make a bunch, and only use a little, no big deal as it will be used up, eventually. Measure, label, and properly store the result, and it should be fine. This is all basically what I remember from the Windy videos. Others will likely chime in differently.

I shot the gold and it looks really pretty. Probably very heavy because I shot over white without the colored base like James mentioned. But it's just some accents, so I'm satisfied with it. Now I just need a tape to hold so I don't get over spray. Other thread for that one.