color: Fix documentation of 'hsla()' parsing

The documentation for the s and l components is incorrect; these have to
be percentage values and must have a '%' character right after the
number.

Based on a patch by: Pablo Pissanetzky <pablo@trickplay.com>

https://bugzilla.gnome.org/show_bug.cgi?id=662818
conform/color: Add more test coverage

https://bugzilla.gnome.org/show_bug.cgi?id=662818