Nether brick along side nether brick stairs,slabs,walls and fences have slightly lighter texture than the cracked and chieseled nether brick. I say the proble is on the normal netherbrick (and slabs, stairs ect) as on the java edition, the texture is dark. Hope that get fixed, cause it ruins some builds' aesthetic. Also, chieseld netherbricks have slitely lighter texture than cracked and they arent directional.
Thank you for your report!
We're actually already tracking this issue at MCPE-15599, so I will resolve and link this ticket as a duplicate.
That ticket has already been resolved as working as intended, which means this is not considered a bug and won't be fixed. Please do not leave a comment on the linked ticket.
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