There are two ways to reproduce this:

• get out a tape measure, scroll until you have the black color, measure a region
• go to C&B's client config, find [settings.chiseling-previews.default.colors], set chiseling to [0,0,0,1] and placement to [1,1,1,0], then hold out a bit and look at a block

For any bug reports please provide the following details as well,

• MC Version: 1.18.1, forge
• C&B Version: 1.2.62
• Do You have Optifine: no

Client Config:
chiselsandbits-client.toml.txt

Screenshots:

Closed in #825 released in 1.2.65