When I started taking care and selling them, I researched how the leaves get variegated. According to articles on the web, they get their colors through darkness. So I enclosed a batch of them in my bathroom for few weeks. Alas! Two pots rot... and the colors? I did not think the darkness has contributed at all. I think they variegate in season. Like that on the photo. It has been outside the house since January. I only took it inside just few days ago when I noticed the varigated leaves coming out.

So yes, your poinsettias will have their colors soon.