First of all, that looks great! I love the colors you chose and that it is a souvenir from a big trip. That’s awesome!
My opinions are below, and like any good (yarn) doc I’ll advise you to get second opinions- so paging Yarn Doctors, paging Yarn Doctors @AIMR @MistressJennie @photojenn.
I can’t remember if Doc @sheepBlue does crochet, but her design eye is legend so opinions there would be great, and same for @Immaculata.
Feel free to tag in others as you think of them, I haven’t had my coffee yet so I’m not working at top capacity. Oh! @Dooney is a crochet master, too. Ok, moving on:
When I make something that has uneven edges (I don’t know why, but for the life of me I cannot work back and forth and get consistent stitch counts!) I do just as you describe- big stitches for wide discrepancies, smaller for less obvious ones. I think you’re less in danger of it being too eye-catching because you’re planning to fold it in on itself anyways.
A great thing about crochet is the ease of experimenting. If it were me, I would probably start by using that green I have the most of and square off my wonky edge and then take that yarn once thinly around the whole to frame the triangle to see how it looks, especially as you mention that you don’t have it represented elsewhere in the shawl so that might be important to you. I don’t have a good pic anymore, but I had to do that with my Mutts blanket seen here on LC and if you zoom in you can tell the black side borders wobble a bit but even at high contrast it isn’t screaming, “she can’t count!”
Then, if I’m honest, I would take pics and overthink it for hours (at minimum) and frog it back to see what the red would look like. That probably doesn’t have enough to go around so it would be a collar-edge only experiment. The red would be more eye-catching, but also looks great with your coloring, and ties in with the four (I think) bands of it within the body of the shawl.
After doing that and taking pics I would scroll between the two versions and overthink both for a while and text my fellow crochet/yarn friends more times than is polite getting their opinions. (You’ll note that I don’t post a whole lot of finished things lol, all my projects take a million years!)
TL:DR- Experiment! Just don’t cut any yarns until you decide. You can try out a bunch of plans to see them IRL and rip them back to try others until ready to choose what YOU love best.
Good luck, and happy yarning!