Sign Up / Log In

I'm stuck and trying to decide on on which color to use for the sign up / log in screen on the new app. The argument: the white background is what we're using on the website, and the dark background is the color of choice throughout all of the mobile experience(s): iPhone, iPad and Android.

In the end, branding matters here, but I think it's just more about conversions. Which one will get more sign ups? Which is more clear? Thoughts?