Steps to reproduce:
1. Open User's attached project
2. Select Main Camera > "Tonempping Color Grading" component
3. Enable "Color Grading" and select "Export LUT as PNG"
4. Disable "Color Grading" and enable "Lut"
5. Load exported LUT to the LUT texture slot
6. Compare exported LUT colors and Color Grading colors in Game or Scene view

Expected behavior: colors look identical or close to identical
Actual result: colors look different

Reproduced with: 5.5.0p3, 5.4.4f1, 5.3.7p2

Note: the issue might be hard to reproduce due to issue when "Export LUT as PNG" exports black image (case: 866593).
The issue is more visible when using green color.