I have a really simple scene with the following set-up:
The first MeshInstance is a big sphere with this shader:
ALBEDO = vec3(0.5,0.5,0.5);
MeshInstance2 is a small cube with a spatial shader, set to unshaded and given a red albedo (all the other settings are default).
The default environment background mode is set to clear color.
It looks how I'd expect in the 3D view:
But when I play the project the cube isn't red, it's the same colour as the project clear colour:
Is there something obvious I'm missing, or is there an issue with my computer? TIA :)