To reproduce:
1. Open a new Unity project
2. In project window, create a Material
3. Click on Material, then open Color picker in Inspector
4. In "Current Brightness" field, put in a number with a comma (for 2,5 for example)

Expected result: Unity automatically changes all the commas to dots, so this field should be no exception
Actual result: on applying a number with a comma, all the fields in Color Picker reset to 0

Note: Writing a number with a dot instead of comma works perfectly.

Reproduced on: 5.5.4p1, 5.6.2f1, 2017.1.0f1, 2017.2.0b1

Fixed by the introduction of a new color picker
Fixed in 2018.1+