I bought my first spool of Aurifil a while ago, loved it so much I immediately placed an order for more colors AND for the color card. The color card has really come in handy!!
BTW - the best prices I've seen online for Aurifil is as
http://www.sewezdesigns.com/Aurifil2.html.
If you find a better price, let me know!
Oh. For colors that blend easy into multi-colored pieces I like: medium grey #2620, dark grey #2625, and light grey #2615 (#2600 is a little too "silvery"), and in the brown/taupe range I like: medium #2326, and light #2312.
These are my "go to" colors when I'm working multiple color fabric (either in one piece or different pieces). Remember that if you have to choose, always go darker as the thread will "hide" better in the "shadow" of the seam. If I want to use colors for quilting, then I match the color to what I want using the color chart.