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The very nice formula in the answer given by JvdV, needs to be dragged down for the rest of the list.

Expanding the formula

You could further expand by trying the following in cell G1

=QUERY(TRANSPOSE(INDEX(TRIM(REGEXREPLACE(SPLIT(TEXTJOIN("+",TRUE,B:B),"+"),"(?:Purple|Blue|Pink|Green)","")))),
            "select Col1, count(Col1) where Col1<>''
             group by Col1 label count(Col1) 'QTY' ",1)

PROS

1. A single self-expanding formula for all present and all future products
2. All products become alphabetised
3. There is no need for the extra column D where to manually write all products. This way you avoid human errors.

CONS

1. The fact that all products are accounted for will be a problem if you want just some of them -like just the notebooks-