I tried retexturing infested stone bricks via a resource pack, however it seems like it's currently impossible without creating other files to change model and blockstate accordingly. This is however highly unintuitive and inconsistent with the way other blocks can be easily retextured. It seems even more weird when once you remember infested blocks have an unique ID so they may as well be other blocks.
If this turns out to be a feature, then this bug report may as well be a suggestion to change it, since as I mentioned it breaks consistency; retexturing said blocks is still possible, just a tiny bit harder, so it remains as a possibly unfair advantage either way.
Steps to reproduce:
Create a new resource pack-ready file eg. by unzipping version .jar file and copying whole assets folder, adding RP desription and icon files, or by manually making the correct directory
Create 16x16 .png files and name them "infested_stone_bricks", "infested_mossy_stone_bricks" and "infested_cracked_stone_bricks" accordingly
Enable resource pack - you should notice that said blocks don't change while most other blocks will.
Attachments:
Pictures with and without the resource pack - I also showed that brown stained glass is properly retextured to prove that it should be working.
A screenshot of resource pack directory and changed texture files
Resource pack I used for testing the bug
I don't think this is a bug. Not every block has its own texture. For example, buttons, fences, slabs and stairs all do not have their own texture file by default but reference an already existing texture in their model files.
I can't think of any other block that doesn't have an own model, but other than infested blocks, I don't know of any block that looks exactly the same as an other one.