>>2. I don't know what color they're being printed on. I am waiting for expert opinion before deciding.
Black is a good color for both illustrations if you want synergy. It's night-themed and classic color
Also purple #66017a and blue #1f084b looks like a good option.
If you want something light, maybe yellow #FCCB37 for the dog and #FFF461 for kiwis, is the color of the corn.
If you want green, you can take the color of the plants and the kiwis.
You can go with classic white but it won't feel "unique and detergent", there's too much visual weight in color, the white makes contrast in both pictures. I perceive it very "corporative" under a white background instead of an urban T-Shirt, dunno, is just my opinion as I'm picky with white backgrounds for illustrations that aren't white.
I'm not an expert but well I think that you should have at least one light and dark color and to combine with the shirt.
You could go white, black, Light color, dark color, 4 designs.
Edit: I saw the colors post just now, well
Nightmarishly expensive is not an overstatement - 39 bucks to get a couple of ounces of shirt to Europe.
(Not flaming Null - just genuinely surprised it is THAT bad)
39 USD?, feels cheap.
I'm going to reveal some of my powerlevel. This is amazon shipping to my cursed country.
Bonus: This is only the price of shipping, without taxes, and without converting my local coin to USD.
If I were to do that, the actual price would more or less double.