Jenn from Endlessly Inpsired shows how she used Kool-Aid to create a dip dye effect on a pillow cover.  It creates a lovely, painted effect on the pillow.  She did this on a pillow cover she made herself, but you could also dip-dye a purchased pillow cover.  Just be aware that synthetic fabrics may not take the dye.  Stick with cotton if possible.  Go to Endlessly Inspired for the tute.

[photo from Endlessly Inspired]