Hello ,
With Color Grading Intensity set to above 0.5 , it is quite difficult to get the result you want , as those Look up textures override the default sky brightness. In my post process blendables pack , there is one Diffuse Light shader that is going to achieve the color grading effect and also keep the sky brightness as desired. Back at the time when I created Daylight system I had no idea how to create Blendable materials , but since you mentioned the issue , I am going to add the Diffuse light shader with Daylight System in later release , so that you have more control towards diffuse and ambient color and intensity.