I have a full grid with the 13 blank cells. I can see the 13 omitted are the same as .....but can't see how to redistribute them or do the colouring in ??
There's a significant phrase at the end of the second-last sentence of the preamble - that and the name took me to illustrations (!) of the theme. Hope this helps.
saladdodger - As you've spotted they're 'the same as...' you must have spotted what to erase.
I then just put them where they should have been in the first place (and coloured either side of the gap appropriately).
I have moved all the letters from 5d into the blank spaces? ....but don't see what to colour despite looking up the artists works. Sorry to be so thick here!