Humm well Captn, them marking all go back to the hey days of us Pirates you see Capt, twas another way to entice Ships onto our shores by stealth and showing false signs, where we could plunder and pillage them, in these days just maybe Councils are doing the same jobby somehow ?
Around the back of islands the ebb can be both directions away from the centre, so colours as per the buoyage direction on chart and thus consistent along general coast but not always as per tide floods at that point. River estuaries and Scottish island channels spring to mind.
