Edit Nov 12, 2017:
The patch for the issue described below has been accepted into Forge and is included in version 1.12.2-184.108.40.2067+.
What are you testing?
Many mac users are probably aware that the Forge splash screen, added back in the days of MC 1.7.10, causes missing or distorted textures when enabled. I believe I have found the cause of this issue and have summited patch to fix it here. However, the Forge team would like some community feedback to make sure that this patch really does resolve the missing textures issue, and I completely agree with them. To aid in this, I have made a mod that is functionally identical to patch submitted to Forge.
So how can you help?
First, you need to have access to a computer running MacOS. Next, you need to have MinecraftForge installed for any version of Minecraft from 1.7.10 up through the latest 1.12.2 (a mod pack for these versions of Minecraft should work too). After this, you need to manually enable the Forge splash screen (an explanation of how to do this is included below). Now, if you run the game and load a creative single player world, you should see some of the item textures missing (not the purple and black texture). They can sometimes be replaced with random or distorted images as well. An easy way to verify this is by navigating to the search tab of the creative inventory (top right tab) and scrolling through the list of items.
If you found missing textures, that is great (well not really :P). Let’s see if we can fix that.
Now, to test the fix you need to download the mod I talked about before and place it in the ‘mods’ folder. The mod is attached below and source code can be found on the Github page here (if you would like to look through it). You should now be able to relaunch the game. If this fix works, then all the item textures will appear properly with the Forge splash screen enabled.
Please leave a reply stating whether or not the SplashFix mod resolved the missing textures for you. I kindly ask that you also include the Minecraft version(s) that you tested and version of MacOS you are using. Thanks!
How to enable the Forge splash screen:
In the Minecraft installation folder you should find a folder labeled ‘config’. In the config folder there is a ‘splash.properties’ file. Open the file in a text editor and change the line “enabled=false” to “enabled=true”. If this file is missing, then you have to launch the game once so Forge can generate it.