Steps to reproduce:

1) Download attached project and open in Unity
2) In the Project window, select "New Material" material
3) In the Inspector window, select the color button (to open Color selection window)
Note: Window to pick a color is not opening

Expected result: Window to pick a color should be opened (check attached image "expected.png")
Actual result: Window to pick a color is not opening

Reproduced with:
2018.3.0a4

Not reproduced with:
2018.1.9f1, 2018.2.0f2, 2018.3.0a3

Regression since:
2018.3.0a4

Tested using Windows 10 machine

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Fixed in:
2018.3.0a8