Vibrant Visuals: gilded blackstone is too bright/desaturated/shiny

Same issue as (MCPE-220761): the gilded_blackstone_mers.tga has 64 added to the metallic (red) channel across the entire block. The metallic channel should be 128 on gold pixels and 0 everywhere else. Instead it is 191 on gold pixels and 64 everywhere else.

Repro: find a bastion and examine gilded blackstone blocks next to other blackstone variants in the walls.

Expected result: gilded blackstone matches the color tone of other blackstone variants.

Observed result: gilded blackstone appears more bright or unsaturated or grey than other blackstone variants.