There is a little bit of color spread here, it's just small. It may be less than there should be, it's hard to say; you should really test on a more neutral surface so you can see properly. To get more accurate GI you can turn up GI Sample Quality. Turning up GI Cache Detail would give you more detailed, nuanced results. You can also turn up Bounce to the Ounce in GISD settings to get a more dramatic effect, though less realistic.
There is a small contact shadow, as it should be. Since you don't have soft shadows enabled, I don't see a reason why the shadow should get darker closer to the spheres. The contact shadow is fairly realistic as far as I can see, it should always be small.
- Oshyan
