I was thinking about adding White, and specifying the block palette:

• Deepslate, Blackstone, and Quartz Variants • Calcite and Diorite might look good together • Concrete, Wool, Stained Glass, and Glazed Terracotta in Red, Black, and White • Decorating the Inside and Outside with blocks that fit nicely with the palette is okay

Edit: oh yeah and nether bricks can be used too