GLTF Exporter isn't compliant to GLTF Validator.
The GLTF exporter produce a texture that isn't compliant with the Khronos GLTF validator :
IMAGE_NPOT_DIMENSIONS
.
This issue is a followup to paraview/paraview#22500.
The GLTF Validator expects a power of two texture and the texture generated by vtk is of size (power of two + 2 ). Those 2 additional values corresponds the 'out of bounds' colors.
It may lead to issues in external viewers trying to read the texture.