How to reproduce:
1. Open the attached "CopyPasteBug" and "SampleScene" project
2. Go to Canvas --> Button
3. Change Buttons normal color (to blue for example)
4. Right click on Normal Color field and copy it
5. Try to paste the Color onto other Color field (Pressed Color for example)

Expected result: Color gets pasted to another Color field
Actual result: Color does not get pasted to another Color field (copy-paste does not work)

Regression introduced in - 2018.1.0a5
Reproducible with - 2018.2.0a2, 2018.1.0b9, 2018.1.0a5, 2017.3.1p2
Not reproducible with - 2018.1.0a4

Notes:
1. Re-opening the Editor solves the issue, but problem re-emerges, once the different color is picked for some Color field
2. No issues happen when copying the Color from one GameObject to another

Fixed in - 2018.2.0b1 and 2018.1.0f1