Meta Keywords
7,523,563 websites

Meta Keywords is free to use

http://www.wordstream.com/meta-keyword

Meta Keywords are a specific type of meta tag that appear in the HTML code of a Web page and help tell search engines what the topic of the page is.

VS

Theme Color Tag
4,102,291 websites

Theme Color Tag is free to use

http://updates.html5rocks.com/2014/11/Support-for-theme-color-in-Chrome-39-for-Android

Chrome for Android, since version 39 supports the "theme-color" meta tag to allow websites control the background color of the tab's UI header.

Market Share by Top Websites

1 Meta Keywords is leading in Top 10K Sites, Top 100K Sites, Top 1M Sites and The Entire Web.

2 In terms of market share, Theme Color Tag is clearly lagging behind, losing to Meta Keywords in all segments.

Websites Categories

1 Meta Keywords has better usage coverage in more websites categories. Including Computers Electronics & Technology, Arts & Entertainment, Science & Education, Games and 20 other categories.

2 Theme Color Tag hasn't got a lead over Meta Keywords in any websites category.

Geography

1 Meta Keywords is leading in most countries, including United States, China, Japan, Russia and 155 other countries.

2 Theme Color Tag is leading in Sweden, Finland, Norway, Iceland and 3 other countries.