I am following along with a tutorial and using Illustrator CS6 version. It mentions a colour mixer but I can't find it. I am wondering if this feature is for later versions? Also if there is an alternative to this in the CS6 version?
There is no Properties Panel in Illustrator CS6.
Therefore there is no Color Mixer option in Illustrator CS6.
However, Illustrator CS6 does have the Color Guide panel, which is similar.
Window > Color Guide to view the panel.
If you are following tutorials, it's wise to be aware that if the tutorial author is utilizing a newer version of the application, there may be many things which are not present in legacy application versions. There isn't always an equivalent to a new feature in older versions.