Scarlet Kale

So I'm growing some scarlet kale through the winter and as you can see the seedling pretty much just looks like regular kale at this point but it is supposed to be a very dark purple (almost black). The seeds were purchased from a reputable source so I'm sure it just takes some time for them to develop that dark coloration. I plan on selling seedlings of this variety at farmers markets but it might be hard to sell if it just looks like every other kale variety. Does anyone know how long it takes for them to start developing the darker coloration?

The description of the seeds say:
 
Remarkably attractive dark green kale with red veined, frilly, tightly curled leaves. A vigorous performer with good cold tolerance. Leaves darken to deep scarlet in late season. Begin harvesting leaves when young, and allow plant to grow well into the early winter. 24-36" tall by 24" wide, 60 days from transplant, Seems the cold is what turns the kale deep purple. Hope this helps! Cheers!
 
You being in socal the kale might not change color at all?

That's why i'm growing it in winter. We do have pretty mild winters but we do get some cold nights. I dunno. We'll see how it goes. This is more of a test than anything before I grow it to bring it to market.