Board Thread:Plants vs. Zombies 2: It's About Time/@comment-26185616-20150305174327/@comment-4024597-20150316074616

I remember someone saying:

The icon for 2.3 update has purple background, hinting Dark Ages.

The icon for Vasebreaker update has purple background, hinting Big Wave Beach.

The icon for 2nd Feastivus has purple background, hinting Frostbite Caves.

What is colorful-egg background hinting?