If you have Sambucus nigra "Guincho purple", that one starts out with green leaves which age to dark purply black, but in shade, may remain green. I'm sure yours will colour up later, particularly when planted out properly.

If it was a cutting (and not seed) then it will be exactly the same as the parent plant. Being green is not a bad thing at this stage as it means more chlorophyll=more food for the little plant. Is it in bright enough light?

Thanks Bamboo and Volunteer I'll move it to a sunnier spot as come to think of it it's not getting a lot of light at the moment.