You get the logo file in EPS format. You can open it on almost any graphic program, select the underline object, and pick a new color from the color palette. It's that easy.
Thanks for all your great ideas, it´s getting really hard to choose! I´d also like som ideas for logos where there´s something in the background, silhuets of leaves or something, try looking at www.musthaves.dk , and look at their logo, thats kindda what I mean :)