FIx color banding in unity

I create archviz in oculus using unity. I didn’t use any texture, just simple solid white color. But inside the room there is gradient from light to dark where i can see the color banding. i’m using baked GI and a single directional light. This banding effect is visible in 3d scene window and when i run on oculus as well.

What setting do i have to modify to fix it ?