I'd needed to put two transparent grids back-to-back to get the "grille" on the back and seat (to avoid problems with backface culling) and was concerned that I'd get a messy Moiré pattern if the two sides didn't align perfectly. In the end it worked out well and I think the shadows set them off well. (Which reminds me that I need to learn a bit about baking shadows at some point.)
For the walls I tried a few different colours & patterns but nothing really worked to my satisfaction. Eventually decided to go for this dark colour with grid pattern, based on the neon/grid motif popular with Acorn Computers -- I'd seen signs done in this style on the Replay Schools retro educational computing stand at the Play Expo and was impressed at how it threw me back into the era of the BBC's Micro Live programme.
You can see how it works in the render below. I experimented with a green grid, which looked too derivative of that whole Matrix black-and-green vibe, and purple/magenta, but in the end this turquoise tint seemed to balance well with the other elements.
Next up is the door and window, with horizontal blinds, followed by the other shelving with records and TV.