white with yellow? White OR yellow? Well for the Dark blue shirt if they're wanting to emphasis the black words- a different light color would be best- gray maybe or Yellow.
It's more or less standard to have the opposite shade/color when you want to put text on a dark color. Same is true for light...
For example- you would never put a yellow text on a white t-shirt- would be way too hard to see/read even for normal vision people. So... black, blue, green, red would work best.
On a darker shirt (say Black or navy/dark blue)- you'd need white, yellow, pink maybe, orange... or inverted colors (I learned about that in my course lol)- like 'neon' teal. If you're curious on that I can post a screenshot on what colors look like on a black background (mainly for websites/apps but good rule of thumb for anywhere else).