The separator between two color pickers is missing when "Random Between Two Colors" option is selected from "Start Color" dropdown under Particle System component, refer attached screenshot

Steps to repro:
1. Create a new project
2. Hierarchy > Create > 3D Object > Particle System
3. Select "Particle System" Object in the Hierarchy
4. Select "Random Between Two Colors" option from "Start Color" dropdown

Actual Result:
The separator between two color pickers is missing on selecting "Random Between Two Colors" option from Strat Color dropdown

Expected Result:
The separator between two color pickers is visible clearly on selecting "Random Between Two Colors"

Reproducible on:
2020.1.0a11, 2019.3.0b9, 2019.3.0a3

Working Fine on:
2019.3.0a2, 2019.2.6f1

Environment:
Windows 10 & macOS 10.14