After 6 coats there is enough paint on the walls. The waviness could be causing the problem by altering how the light hits the wall. Another possibility is how the paint was rolled on and if the surface has any texture. If the paint was dry rolled, not applied thickly and quickly without going back over as the paint starts to dry. Dry rolling causes more paint to take on the texture of the roller and the direction of the texture, rolling up the texture points up – if rolling down the texture points down. This is also a problem for smooth walls or walls with very little texture.
You don't mention the color but the color is affected by how the paint is applied, just like above.
Allow the paint time to fully cure before try another coat or color. Curing takes 2-4 weeks.