Since you already have a Galet GGH and your collection consists of mostly neutral colors, Amethyst would be a great addition. Since GGH and the Hobo style are both discontinued, you might have a hard time finding it later on if you change your mind.
But I would pick the Galet SGH Day because I like the shape of the Day better than the Hobo and Galet looks great with SGH. GL with your decision!
if i remember correctly - you have a couple of galet pieces in your collection already? i would go for the Amethyst GGH Hobo as it gives your collection a pop of colour and it's so much prettier than Galet GSH.