I've done the black and white thingy to put them in order but are these even the same colour?
The photo is too small to see well but the second from bottom looks to be leaning towards purple (warm blue) whist the others are a cooler blue, leaning towards green. Also the fabric at the top is a greyed down tone of the cooler blues.
They are certainly not in tonal order (light to dark) in that photo.
Photos on a Mac has three b&w options; mono, tonal and noir.
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Going from the top down I would say that 2 is the darkest, then 3, then 4, 1, 5 and 6 is the lightest.