Re. size, I think it depends on how much you need to carry. I'm also 5'6, and have the PM. I tried both on in the store, and the GM looked fine, but the PM was perfect. The GM wrapped around my body a bit more. The PM looked sleeker. That said, I'm thinking of getting a GM for winter, when I need more room for gloves, etc.
For color, I think H does colors so well, and the Evie is one of those bags that, to me at least, looks better in color (unlike, say, a Kelly that looks great in black or color). There are lots of colors that are dark or deep enough that you shouldn't have to worry about color transfer: Blue sapphire, Graphite, Chocolate, Malachite, Rouge Garance and Etain all come to mind.
I'm one of those people who never thought I would like this style and now that I have one, it's one of my most used bags! Let us know what you decide!