That's a cute purse! I see now it is not quite what I was picturing - although I did search around in Google for modular knitting yesterday.
I have a pattern for a similar type purse, although it's just one big hexagon shape - you make the first triangle by casting on an odd amt, then on all odd rows do a k2tog at both ends and do a s1, k2tog, psso in the middle, eventually decreasing down to 3 or 5 st. Then you pick up along the side and make another triangle. You wouldn't be able to make the color changes like KnitSimple shows unless you picked up along your cast on edge, but a multicolored would be nice and make the changes for you if you did the side pick up!
The Brea Bag
might give you some ideas - you could omit the cable and just make each row with a couple more sets of the pattern stitch, then seam together to complete a hexagon shape.
I also found this
little tutorial, very similar to the link from yesterday but pix included.