Joel:

If it wuz me, I'd probably use:

Sher-Clear 1K - Acrylic Clear Coat - Protective & Marine

or competitor's equivalent.

Yours is a small mural, so ask if it comes in quarts, and put on the whole quart in multiple coats. Or, see if anyone makes an acrylic clear coat in quarts.

PS #1: That web page says: "1K - Acrylic"

"1K" is just paint speak for "one component" which means it air dries just like house paint. "2K" would mean "two component" like epoxy where you have to mix two parts of the coating together before applying it.

PS #2: That web page says: "Waterbased Fade-A-Way Dye Additive available"

I suspect what they mean by that is that they'll put a "leuco" dye in the stuff if you ask for it. Leuco dyes are a family of dyes whose molecular structure changes depending on their environment. Leuco dyes were the flavour of the month in ceiling paints a few years ago because they'd go on light pink or light blue, and dry white. That was just because as the paint dried, the dye was exposed to fewer polar water molecules and the leuco dye inside the paint would respond to that change by changing it's structure so that it no longer absorbed blue or red light, respectively. Eventually, leuco dyes tend to become stable in the configuration that doesn't absorb any frequencies of light, so they remain colourless so as not to affect the colour of the ceiling paint or wall paint.

(Phenolphthalein dyed paper, which we all used in high school to tell if a liquid was acidic or basic are probably about the most familiar leuco dyes to most people.)