I find the unrelieved use of netherbrick (block, slabs, stairs, & fences) in nether fortresses consistent with the [assumed] dark and brooding nature of the structures. [Very suitable for a hell dimension.]
Rather than using red nether brick [RNB] to decorate the current structures, I'd rather see a small chance that a particular nether fortress was constructed of RNB thus adding some variation while preserving the grim-dark nature of the sites …
While this would involve adding RNB slabs, stairs, & fences, these would be useful additions in any case (and a small positive step in adding additional slab, stair, fence/wall variants).
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WARNING: I have an extemely "grindy" playstyle; YMMV — if this doesn't seem fun to you, mine what you can from it & bin the rest.
Add chiseled, cracked and fence variant for red nether bricks. Also blue nether bricks, with a color from the warped forest with the same variants should be added based off of warped wart from warped wart blocks. Also tile variants and stairs/slabs/walls should be added for all of the nether bricks. Chiseled red nether bricks would have a piglin snout or strider face and blue nether bricks would have an enderman face.
Here is a picture with all of the textures and a smaller one for you to download to extract textures for your mod if you want to, but please give me credit.