Here's a higher-res version of the tiny thumbnail you linked for Numa:
And more on Numa:
It looks like Mehron Paradise Teal
will get you pretty close to the highlights.
However, you're also going to need to contour and blend with a darker color. Look at the color swatches in that concept art; her lekku have a color gradient that goes to a darker blue, and that color is also used as a shadow to contour her cheeks, under the jawline, and to shape the eye sockets and nose. You might be able to mix up some Mehron Blue with the Teal to get that contouring. For the lekku, you'll (hopefully) only have to paint them once, but for your face you'll need to do it up every time you wear the character.
Or, do the base color paint with the Mehron Paradise Teal, then contour your face with dark-teal pigmented powder instead of a second color of paint. In fact, that's probably what I would do. Powder-over-paint may not work well on the lekku, though.
Note that everyone's skin is different, so the products will go on a little different a look at little different on every face. This might be something that you'll need to take those reference swatches to an in-person makeup expert, and have them help you pick products that will work well with your skin.
Then, practice applying it at home when you don't have a time limit. Practice a couple of times until it looks great and you can do it quickly. Don't try to figure it out the day of the con.
Also, I'm planning to have Kanan Jarrus done by Star Wars Weekends in April, and my wife is working on Hera