try this method with spinach or anything really dark green
http://www.scienceprojectlab.com/easy-s ... phyll.html
for the solvent use either rubbing alcohol (isopropanol) or acetone (nail polish remover). Or get a bottle of everclear as solvent (ethanol)
Ian has the right idea by just boiling down the mixture with water, but this might be a little faster.
Also remember you will be boiling off most of the solvent before you add it to your soap, but you might have to leave a little bit in to make your dark green syrup extract remain liquid and pourable.
I don't think there will be a reaction between the soap and the acetone, soap is a relatively stable molecule and as long as the temperature is relatively low the acetone wont react or decompose.