The answer: a moderate pain in the ass.
The colored bread didn’t end up anywhere near as vibrant a blue as I wanted. My white panel squares had a bit of droopage, though I think I figured out some ways to fix that. Creating evenly spaced squares in the medium of bread dough is clearly going to take some serious practice and patience. Next time, I need to make twice as much dough in both colors in order to get the full effect. Oh, and use an entire freaking bottle of blue food coloring.
If you’ve seen a better Tardis bread out there, link me to it. I’d love to see what a more experienced baker recommends.