Steps to reproduce:
1. Open new project
2. Create a plane and bake a navmesh for it
3. Set intensity of directional light to about 50~
4. Rotate the light throughout the whole cycle
5. Observe navMesh preview getting blown out along with the rest of the scene

Expected: NavMesh preview should ignore lighting, you should be able to see it in the darkness and the absolute white of intense light.
Actual: You can see the navMesh preview in the darkness, but when light blows everything up to absolute white, NavMesh preview is lost

Notes:
- Seems to be Windows and Linux only
- The issue is more visible as the intensity of light is no longer constrained to 8. Currently, it is unlimited and it can cause overbrightness.
- Reproduced in: 2017.1.0b6, 5.6.1p1, 5.6.0b11, 5.6.0b1
- Issue introduced in: 5.6.0a1
- Does not reproduce in 5.5.3p3, 5.5.3p4