Purple with green in the center I wouldn't worry about, all green with no purple might indicate a reversion. Wait until the leaves have fully expanded before you decide there is a problem.

What is the soil like and what, if anything, did you do to amend it? My 'Summer Wine gets shade starting at 3-4 ish this time of year and I don't recall seeing that shade of green lately. Might have when I first planted it, but I don't recall. As bboy said, you have purple and that's a good thing.

tj

I spoke to Sooner Plant Farm where I purchased this Ninebark from. They told me that the new leaves emerge green but turn purple as they age. I don't know if this is accurate or not, but they haven't misled me yet. I will give it some time like bboy suggested.