How do I change the clock font on my lock screen?

[Android Central Question]

My phone has suddenly updated to using Samsung Themes today, and I can't figure out how to make the text on the lock screen black with one of my photos as the wallpaper. It used to do this automatically, and the photo I use is white where the time appears so I need the text to be dark. I have already applied a theme whose lock screen text defaults to black, but when I add the wallpaper photo it defaults to the lettering being pink & purple, which is hard to read.