QBASIC color numbers

According to QBASIC.HLP color numbers are in the range 0 to 15.
However I've come across several QBASIC programs using the statement
'COLOR 23' (even Microsoft's own REMLINE.BAS). Can anybody tell me
what that does, and where I might be able to find a more accurate
description of QBASIC colors and graphics than can be found in

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