Actually I have SD4500,I think SD4500IS has same functions as SD4000IS Here is the Way to use Color accent and color swap.. color Accent: Choose color accent mode. Hold menu key for few secs and release(do not just press). At the bottom color selector will appear-- Focus camera on object.Adjust the rectangular color selected(BOX) on color you want to be accented. press left navigation key on wheel....Now color to be accented is selected...U r ready to capture the image.
Color Swap. In the same way you can find out color SWAP. Its really easy.