bug#25890: `color-values` gives wrong value

[Eli Zaretskii]

> From: "mail@yo.eki.do" <mail@yo.eki.do>
> Date: Fri, 10 Mar 2017 08:33:59 +0000
> 
> This change will have too large impacts since the number of parameters
> will change.
> Indeed developers can use the optional argument, but that trick won't
> work in the previous version of Emacs and will lead to
> wrong-number-of-arguments errors,
> so they will need burdensome workarounds e.g. version check.

Packages that need to support older versions of Emacs will have to
provide a wrapper function that indeed looks at emacs-version.  That's
nothing new.

> I'd have to say that the default argument should stick to 2, the original.

That would leave the original problem in place, so I don't think it's
acceptable.