"Toning" in most cases is NOT desireable on coins ... that's why many coin dealers "dip" their toned coins in solutions designed to remove the toning.

As for rainbow toned Morgan dollars ... these have naturally toned over a period of 100+ years ... not stored in capsules which have leaked air through isolated cracks such as silver strike cases have. Yes, there are coin collectors who seek out toning on coins, but most coin collectors like them BU without toning. As in silver strikes ... it's a matter of personal preference.

Also, along the same lines ... while slabbing is widely accepted in the coin hobby ... "slabbing" is generally thought of as abhorent in casino chip collecting, Different strokes for different folks.