I am making a resource pack, and the textures I edit are all appearing as pink and black. Entities aren't affected by the missing-textureness but all the blocks I edit are. I'll send the pack if needed.
The black and pink squares mean that the texture is missing. The only reasons I could think of for that would be:
You're using a transparent texture
You're not saving the file correctly
You're using a non recognized format (Something other than .png or .jpg, maybe something not recognized like a .svg file)
Other than that I don't know. If that doesn't work there are some amazing youtube videos out there for just this question. Another cool thing you might want to look into if you fix this is "Damaged Item Variants." I found the best video from a guy named samasaurus6. He actually has an entire series on texture making you could look at.