Sure. If you need the full background on NES graphics, I think this is a pretty good description: https://taywee.github.io/NerdyNights/nerdynights/backgrounds... But in a nutshell, tiles on the NES are 8x8 pixels, but they only carry two bits of color per pixel. Another two bits ("the palette") are added from the attribute tables, but the attribute tables are pretty small (to save on memory of course) only containing two bits for each 16x16 pixel area on the (virtual) screen. That's why background graphics on almost all NES games are built out of 16x16 blocks. What they've done here is they've added on-cart memory to expand the attribute tables to the point where each entry corresponds to an 8x1 pixel area on the screen. Essentially allowing every row of pixels in a tile to have its own palette. It must be a bit of a weird constraint for the artist to work with but it's obviously superior to just having one palette for every 16x16 block of pixels. The interior scene, and the bookshelf in particular, shows it off really nicely.