Short description of error
Sculpting mode doesn't show the material the same way we see in object mode.

Exact steps for others to reproduce the error
Create a sample file from scratch by:

• Add an UV for the cube
• Create a material
• Add an UV Map node
• Conenct the node to the Base Color and Emissive Color.

Or open:

Now switch from object (or edit) mode and sculpt mode. In sculpt mode the UV is black.