You could use the shorthand, but it's really not necessary at this point. The spec is (unsurprisingly) quite [specific][1] that this color value is exactly "#6

You could use the shorthand, but it's really not necessary at this point. The spec is (unsurprisingly) quite [specific][1] that this color value is exactly "#663399". All browsers which implement CSS Colors have had support for years now and the Color Module itself is now a CR as of a year and a half ago. Incompatibility isn't exactly a rounding error yet, but we're close. [1]: https://lists.w3.org/Archives/Public/www-style/2014Jun/0312.html https://lists.w3.org/Archives/Public/www-style/2014Jun/0312....