Why is it called a LATICRETE® 600 Series, Un-sanded grout?

It is called LATICRETE® 600 Series grout as it is has many colors available as variants to choose from and the first digit starts with 6 and ends with the number code of the color. For example, LATICRETE® 645 stands for Raven color and LATICRETE® 644 stands for bright white color. All the color variants have the same physical properties when used and
don’t differ in performance. It is called un-sanded as it is used to fill narrow joints up to 3mm width.