How to reproduce:
1. Open the attached project (created using the Lightweight RP template)
2. Open the Tile Palette window
3. Create a new palette
4. Drag and drop a few tile sprites from Assets/Sprites into the Tile Palette

Expected result: In Project window, the newly generated Tile Assets are displayed in the same color as the sprites from which they were generated.
Actual result: In Project window, newly generated Tile Assets are displayed darker than they actually are.

Reproducible with - 2018.1.4f1, 2018.2.0b6, 2018.2.4f1

Notes:
- The issue is reproducible on projects, created with templates, other than "2D" or "3D" (i.e. it is reproducible when created with templates: "3D with Extras", "High-Definition RP", "Lightweight RP", "[XR] AR Basic", etc.)
- Not reproducible on versions prior to 2018.1, since new project templates, on which the issue is reproducible, were introduced in 2018.1.

Fixed in 2018.3.0a1