Visual effect of loading screen is jarring

**Is your feature request related to a problem? Please describe.**

Currently loading scrren has a light-colored cover.

When annotating on **dark-colored** images, the appearance and disappearance of loading screen would cause screen lightness switching very quickly. Over time that makes eyes feel uncomfortable.

**Describe the solution you'd like**

Weakening or removing visual effect of loading screen cover.

**Describe alternatives you've considered**

Adding a slower animation on the appearance and disappearance of loading screen cover to make it not that jarring.

**Additional context**

Screenshot of loading screen cover