I received a bonus packet of ten "Debutant" variety yarrow seeds when I placed a seed order one year.  Five of the seeds grew into plants.  Two of them were a pale yellow, two were a grayish-white color, and one was purple.  I didn't like the white and yellow ones, and pulled them out.  I kept and propagated the purple one.  The foliage on this plant looks great before it starts to produce flower stems.  The only thing I don't like about this plant is that the stems are weak, and bend down to the ground under the weight of the flowers.  In 2003, I tried trimming back the stems with hedge trimmers before the flowers appeared, in an attempt to make the plants more compact.  It worked, but they still bent over more than I'd liked.  In 2004 I cut them back a little more severely and wound up with very few flowers.  This yarrow doesn't have invasive, spreading roots like some other yarrows do.