Well it's better to use the same brand and type paint since it would adhere better. Kind of like compatibility. Using different types of paint base and or surface use will not be good for many thing can happen like decrease in adhesion, change in color, bubbling, or not adhering to each other at all.
So for you research some different brand of paints since some makes good particulay paint. Make sure you use paints that are good to adhering to plastics, and not just that. Make sure the paint have good qualities to work with plastics and don't get damage from bending, expanding and whatever plastics do.
So for you stick with plastic surface primers, paints and clear finish. Find a manufacturer that offers all of this and color qualities as well.
For the under-layer color. What ever you choose under the metallic blue wether it's purple, green or yellow, applying it has also many factors. It's really up to you since applying thin, thick or several coats of under-layer color can also produce different results in the final metallic blue color, vibrance and hue. Also the metallic blue (final color) can also be applied thin or thick or several and have different finish in relation to the under-layer color.
Sometimes if you do it just right, you'll get a chamelion effect as the color can change to different hue of metallic blue or purple (or the under-layer of your choice) or combination of both when looking it at different angles, lightings, shadows, reflections and types of lighting. It's really cool. But you can buy this kind of paints anyways, which are expensive as to compare to a regular paints. Also the clear coat can produce different results in different thickness or layer.
Like I said do a practice coat with a similar plastic of the Xbox 360 and then decide what best for you. And do it safe most importantly and don't breath that paint, it'll get you high and kill some of your brain cells.