When we used Kit-Kat on our devices we had the Xperia Clock widgets on black color, even on Lollipop 5.0.2 we had the black colored clock widgets. But after Lollipop 5.1.1 Sony Mobile removed the black colored Xperia clock widgets. Don't worry, a XDA member Dadovvv has successfully made black colored Xperia clock widgets and even with more colors.
This can be installed on any Sony Android 4.4+ device with Root or Without Root. You just have to install this as a normal apk and then add it to your home screen from your widgets. Keep in mind, this clock doesn't has the Analogue clock. Download the Clock colors from below links
Black with White Shadow - Google Drive
Sea Blue with White Shadow - Google Drive
Red with Black Shadow - Google Drive
White with Black Shadow - Google Drive
Blue with Red Shadow - Google Drive