Problem:
You got the Boox Color 7 as an upgrade or alternative to the Kindle Color but you can't set your sleep or power off screen to the title of your active book
Cause:
It's a built in feature of the Kindle devices and they can't control your Boox Android system...but you can.
Resolution:
Go to Settings - GESTURES area and make one of the swipes (I prefer swipe from left) the Screenshot option (NOT THE AREA SCREENSHOT). Then, open your Kindle app, view the cover, and swipe with your single finger from whichever direction you just set and wait a couple of seconds. When the screenshot menu appears, just tap the check mark. Finally, go to the Gallery app, open screenshots, tap your cover, and tap the More at the bottom right and choose Set As to set your book cover as Screensaver and Power Off images.
I know it's a couple of steps, but really not bad unless you're a speed reader or you read multiple books at a time and want it automatic...to that I say buy a Kindle.