(Caron Yarn) Cakes, anyone?

Michael's had a sale on yarn cakes last week.  I had a great idea to get two as identical as possible (for some double-stranded slippers I want to knit).
In the middle of the night it occurred to me that yes, the strands would "color out" about the same; but each slipper would be different and wouldn't look like a matched pair.

I laughed at that one and don't really know how to remedy it. Sigh.  The perils of the imagination....