Flash of the unstyled background for each color paper-item

[KeithHenry]

Description

When the colour swatches drop down is opened there is a flash of the background colour.

Expected outcome

The panel should expand without the apparent jank.

Actual outcome

A flash (around 1/5s) of the background colour of the .color menu items appears before being overlaid by the absolutely positioned .color:after.

Live Demo

The issue is observable on the main demo https://www.webcomponents.org/element/PolymerElements/paper-swatch-picker/demo/demo/index.html

Here is a mid transition screenshot from that demo:

Browsers Affected

Observed in Chrome, not tested yet in all browsers

• [x] Chrome
• [ ] Firefox
• [ ] Safari 9
• [ ] Safari 8
• [ ] Safari 7
• [ ] Edge
• [ ] IE 11
• [ ] IE 10