The Select node merges two 3D textures by assigning all samples to its first input except those whose color index match the color parameter.
The Select node accepts two 3D texture inputs:
the default texture, used for all samples that don’t match the color parameter
the selected texture that is assigned to all samples that match
The Select node generates a merged 3D texture.
The Select node does accepts 2 parameters:
a color index that is compared with the color index of each sample
a tolerance value used when comparing the color parameter with the sample’s color index