Try using the Z5's light theme. It changes the color of the clock
Sent from my D5833 using XDA Free mobile app
I don't really want to change my phone's entire theme just to get a dark colored clock on the home screen, in my opinion that's kind of insane. Since we're discussing workarounds, I've downloaded an app called "Digital Clock Widget Xperia", it's free (ad-supported), and highly customizable - for instance, you can set the text color to literally any color you like; you can also change the time/date display format. It's basically an improved version of the stock clock, you can definitely set it to look exactly like the original thing, or heavily customize it. I'm pretty satisfied, now that I have it I wonder why I never bothered looking for an alternative before. The ads only appear when you open up the settings, which is reasonable. Leaving this here for people who have the same problem as me.