Shadow, shows descendant on color?

Hi there
I have an issue, in that my shadows, appear on the ground, depending on the color of the ground.

The ground, non matter the world type, uses the same material. The only difference per world is the color of the material. is a single material, which I change to reflect the world it is in, (white= Snow, green = grass, deep purple = night... etc).

So the issue is that the shadow, does not appear (in mobile on a few of the colours). Shockingly, on white (snow) it is very faint, but on deep purple (night) it is fine.


Any ideas?