GAF Timberline American Harvest Series, Golden Harvest Color
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Adobe Sunset would be a riff on the current color, but with much more depth.
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If the owners are buying the shingles, I'd bump in some additional money and upgrade to one of the Designer Series.

Woodland Series, Woodberry Brown
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Cedarwood Abbey
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Country Mansion Series, Weathered Wood color
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Grand Slate Series
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Weathered Wood
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I like the woodberry brown.

You can't go wrong with black or a dark gray--these colors are timeless and will go well with your house, now and in the future, should ever decide to change the exterior appearance with new paint, etc.

Are new gutters and downspouts included? This is the time to economically replace them if needed. If not, be sure the existing are still servicable. If yes, consider copper colored aluminum ones, and ditch the white which call much too much attention to themselves. Good luck!