Hi again, interesting conundrum. If you are using a light to cast the shadow:
Duplicate your object and make it into a solid black/blue silhouette (don’t know what your object is so can’t assist there).Put it below your object layer – parent to original if necessary. In it’s material options set Casts Shadows ON, Light Transmission 100% – it will now cast a blue/black shadow.
On your object layer set it’s Casts Shadows to OFF.
Now play with the colour of your silhouette till you get a colour match.
Should do it!?