Problems with colour pairing

Two-colour brioche: why is it so bloody hard to pick two colours that work together ?

It seems so easy when you start off with your great pattern and your two colours of whatever yarn you’ve chosen … They look so good together in your knitting basket – can’t fail to be terrific.

But they do.

The reverse side is just – wrong.

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Why on the front does the green vertical row sit proud and the violet row provide merely background; and on the reverse the green is competing with the foreground violet...