So I have just started trying to recreate this effect in Affinity. It definitely helps to have the right image, and although I do quite like this one of the boat and it was the best of the batch, it isn't quite right so I am still looking for a better one.
You definitely need an image in which all the grey is removed so you only have pure black and pure white. You then select and fill the black with blue. I have Googled this grey question and it seems like Affinity does not have the ability to remove greys in any sort of effect so it really has to be done in the normal settings. This means it helps if you already have a very high contrast image like this one was. Unless you know different?
I have managed to get the blue bleeding into the white like an ultramarine glaze on porcelain white which I am pleased with so I feel I am getting there.
This one below was a bit of fun because the tree is the traditional Japanese pruned type and has the right look and even though the tower block is in Tokyo and has a Japanese design aesthetic it looks way too modern for the "Willow Pattern" look. But I enjoyed doing it.
This one below of seaweed also doesn't work but I actually really like it anyway, it just makes a nice abstract image.
As teacher might say, "it's a good start but more work needed".