[ purple ]

[ green ]

[ blue ]

[ 2 pairs of purple ]

[ 2 pairs of blue ]

[ 2 pairs [blue + green] ]

[ 2 pairs [blue + purple] ]

[ 2 pairs [green + purple] ]

[ 3 pairs [blue + green + purple] ]

[ 3 pairs [blue + blue + purple] ]

[ 3 pairs [purple + purple + blue] ]

[ 3 pairs [blue + blue + green] ]

[ 3 pairs [green + green + blue] ]