Explain your idea

In the newest version for 1.20.1 (1.20.1-10.1.0-171) the tank texture for the bottling machine is not able to be changed by a texture pack. Every other machines JEI can be modified by a texture pack.
Example where every image in the "texture" folder for IE and JEI is replaced by completely red images:

Changing this, by making the texture for the tank in JEI an imgage, greatly reduces my stress level every time I look at this JEI page when I use a texture pack.

Looked through the code, the slot here is manually drawn directly by code with the specific colours, as well as a few other slots. The water inside uses the textures of the actual liquid, so that's probably fine. If you want to change that, just change actual water too.

Maybe switch to the nine-slice system? Would also fix the accuracy, there should be a pair of #8B8B8B pixels in the other corners.