Full Idea
If we have two cloths of the very same shade of redness, we can show there are two cloths by burning one and leaving the other unaffected; we show there are two cases of redness in the same way: dye one blue, leaving the other unaffected.
Gist of Idea
Two red cloths are separate instances of redness, because you can dye one of them blue
Source
Keith Campbell (The Metaphysic of Abstract Particulars [1981], §1)
Book Reference
'Properties', ed/tr. Mellor,D.H. /Oliver,A [OUP 1997], p.126
A Reaction
This has to be one of the basic facts of the problem accepted by everyone. If you dye half of one of the pieces, was the original red therefore one instance or two? Has it become two? How many red tropes are there in a red cloth?