I went with the reduction method. I figured I could make several colours for the first layer before cutting it off and printing just the black parts.

 I have to say, I got a little carried away and now have 15 butterflies on my desk of various colours and quality :D I also tried different colours of paper just to see how the colours look against different backgrounds. 

 At first I thought of throwing away my faint blue attempt but after adding the black outlines I liked how it turned out.