Actually, I think this bag will look awesome on brunettes (Being one myself). It looks best against blues, greens, browns and aubergine. I also really like it with greys. It looks good with warm colors, but it also looks really good with cool tones. I think that's why I could consider it a true neutral. The only thing I am not too fond of it with is corals/pinks.
I don't think the trouble with this color is its versatility, but that it is probably not the color most people were expecting.
As far as it looking good with SGH, its hard to say. So far, I've been pleasantly surprised at how good the warmer colors look with the silver hardware. It may turn out to be a stunning combination.
Its definitely more yellow than the pumpkin. If pumpkin and mustard had babies, it would be the marigold.