To reproduce:
1. Open a new project
2. Open lookdev

Notice that there are warnings in the console:

Look Dev is designed for linear color space. Current settings is gamma color space. This can be change in player settings.
UnityEditor.DockArea:OnGUI()

Look Dev switch rendering mode to deferred shading for display.
UnityEditor.DockArea:OnGUI()

Look Dev switch hdr mode to on for display.
UnityEditor.DockArea:OnGUI()

They should be:

Look Dev is designed for linear color space. Currently project is set to gamma color space. This can be changed in player settings.
UnityEditor.DockArea:OnGUI()

Look Dev switched rendering mode to deferred shading for display.
UnityEditor.DockArea:OnGUI()

Look Dev switched HDR mode on for display.
UnityEditor.DockArea:OnGUI()

Reproduced on: 5.5.0b1
Not tested on earlier versions because it's a new 5.5 feature.