Finally time to get around to reporting this - I've been holding on to this one for a couple of years at this point. Closely related to MC-236474 (which is not a duplicate), MC-129826 and MC-214662.

The bug

The three arms that come off of brewing stands appear darker than they should due to the absence of '"shade": false' entries for these elements.

This was originally reported under MC-68302. Since three cases of this have been split off into other tickets (MC-129826, MC-214662 and MC-236474), this is following suit, as it's fixable via models only (unlike the mushroom case, for example, which is reported under MC-248703 and is a rendering issue rather than a model issue).

How to reproduce

This can be done easily by comparing a brewing stand (clearest if bottles are present within) in 1.7.10 or earlier to one in 1.8 or later. The older brewing stand will correctly have the bottles appear bright, whereas in modern versions they appear dark.

How to fix

I have attached two resource packs to this ticket to fix this issue. The "45-degree fix" is the simplest one, and is designed to work with the current model. It functionally only changes the arm models to include the parameter that disables shading. I've also cleaned up the model code and added a missing cullface parameter to the middle rod.

There is also a "60-degree fix", which rotates the arms to be at 120-degree angles from each other, which is another thing that changed in 1.8 (MC-257054). However, as Minecraft: Java Edition does not currently support rotation values in increments other than 22.5 degrees, the game's code will need to be modified to permit this. The screenshots of this model were taken in 1.16.1 using the ModelsUnlocked Fabric mod to permit this.