Using the Phisical Sun and Sky is meant to give realistic results for rendering, but it also seems to wash out all the colours. This is apparently due to a gamma value of 2.2 that gets applied twice. I’ve tried to fix it using a few lazy approaches (such as in post production) but came to the conclusion that there is only one way that seems to work – the proper way, aka linear workflow.
To make the sun and sky, go to Render Options and choose Mental Ray as the renderer. In the Indirect Lighting tab, click the Create button next to Physical Sun and Sky. (Once you hit Create, the button text changes to Delete – which you can press if you want to get rid of the sun and sky.)
When you render your scene, the colours look washed out like this.
To fix this, you need to add a Gamma Correction to every texture you use in the scene. To do so, you need to do the steps below to all material nodes in the Hypershade.
Right click on a material node and select Graph Network.
Delete the link between the texture file and the very last material node.
Find the Gamma Correct node in the left hand list labeled Create Maya Nodes under Color Utilities and middle mouse drag it to the Workspace.
Middle mouse drag the texture file node onto the Gamma Correct node and select value.
Middle mouse drag the Gamma Correct node onto the last material node and select color.
Click on the Gamma Correct node and in the Channel Box, change the three Gamma values to 0.454 (the inverse of 2.2).
You need to add a Gamma Correct node to every texture you have in the scene. There are mel scripts out there that automate most of this task for you.
Once you’ve added the gamma correction to all textures, the render with Physical Sun and Sky (in its default state) looks like this.