how would you create this look on a cake? Thanks
Printed edible images.
It's not an edible image - if you look closely you can see some minor flaws in the fondant application.
It is fondant diamonds applied in two shades of red over what looks like a white fondant covering of the cake.
I did a similar one. I covered the cake in ganache and cut out fondant diamonds, then stuck them on with tylose glue. My diamond cookie cutter happened to be the right shape as the angles have to be correct in order to join without gaps.