Custom return color for missing UDIM textures

Blender shows a fuchsia color for missing textures, even textures that are part of a UDIM set. I'd like to request the option to select a custom return color on the image node, to override the fuchsia error color.

For large VFX assets, it's not uncommon to leave out UDIM tiles in certain texture sets for optimization, and simply set the default color to the neutral color of that texture set. Black for masks, blue for normal maps, etc.

For example, say you have a black and white mask that only has content in one UDIM tile, because it's only targeting a small area of the model. Instead of creating potentially upwards of a hundred empty black files for the rest of the UDIM tiles, you'd just not create files there in the first place, and set the missing texture color to black.

This also helps to cover situations where adding new geometry and thus new UDIM tiles to an existing asset requires backtracking across all existing texture sets to add new empty dummy files, instead of just relying on the default value from the image node.

Creating empty dummy files clogs network transfer speeds, when we're sometimes talking thousands of individual texture files, even AFTER culling empty UDIMs.