what are the chunks of the backrooms that look weirder than the normal yellow called

They’re usually called Backrooms levels or just levels , and the weird non-yellow chunks are often referred to as other levels or sub-levels in fan lore.

What people mean

The classic yellow area is usually Level 0 , while the more unusual areas with different colors, layouts, or vibes are other numbered or named levels. In fan discussions, people also casually call them variants , sections , or different realms , depending on the creator’s lore.

Simple example

For example, a bright white office area or a dark damp hallway would usually be described as a different level rather than part of the normal yellow room space.

TL;DR

If you’re asking for the general fandom term, the answer is levels.