How to reproduce:
1. Open the attached Test.zip project
2. Go to Edit -> Settings -> Player -> Other Settings -> Color Space and change from Gamma to Linear
3. Select "New Material" from the assets then go to Inspector and open and inspect the Color Picker palette
4. Go to Player Settings again and change the Color Space from Liner to Gamma
5. Open and inspect the Color picker palette

Expected: Color Picker shows appropriate values
Actual: Color Picker palette has graphical artifacts

Reproduced on: 2018.3.0b1
Not reproduced on: 2017.4.11f1, 2018.1.9f2, 2018.2.8f1