I don't know if the is a pack issue or an issue for you to solve. I'll report it here anyway.
GregTechCEu Modern recently updated to 1.3.1 and in so doing caused issues with textures on Multiblocks. Unfortunately, Gregtech Revival has been affected by these changes.
It mainly seems to affect hatches and buses which appear as a different shade to the surrounding blocks of the structure.
I'm playing Monifacrory but I see the same issues in the GregTechCEu Modern Community Pack withy 1.3.1.
GregTech Revival 32x 1.19.2-1.20.1-1.21 ver 0.11
By the way, your pack is still on 0.9 on Modrinth.