I can change the shadow color (on the Plane/Floor), but I can’t find a tutorial or an option in C4D for this (on the Sphere). I tried in the material and the light. But maybe I miss something…
Not on the Plane.
On the Sphere!
There are various ways to do it depending on the exact effect you’re after.
You can duplicate your light and in the duplicate light set “ambient illumination” on, then play with the shadow colour (Note : one light will affect diffuse and specular, the other the unlit area).
You can also simply add an environment object, and an environment color (it will affect every dark area in the image)
For the most control, you can use a material with a cel shader in the luminance channel. Set it to react to “Light” (instead of Camera by default) and you can define the exact color gradient you want from light to shadow.