I made an attempt but not sure if it will work in your true setup.
I made the calculated field INDEX() and put that on the color shelf
and set the Compute Using to Product.
I added new Products and it seemed to increment the color of blue.
The standard color legend for a continuous is just the color bar,
so I made a sheet to look like a discrete legend. You could put
them all on a dashboard and use a Highlight action to make it
behave more like a standard legend.
Please see workbook v10.3 attached in the Forum Thread.