By default it will turn itself off after two days, but it still sleeps pretty completely without a bunch of idle power draw without doing that.

It has a pretty long battery life with no backlight and airplane mode. If you do a bunch of downloads or run heavy apps and have the backlight high, it will drain faster, but it depends how you use it. Boox pretty aggressively limits background behavior by default, though you can change some of it to allow what you want. I don't have benchmarks or anything to give you a direct comparison, but I rarely think about battery. You're right to raise it as a question, though.

The one thing with color specifically is that it needs more light than black and white to really shine. In bright sunlight it looks great, but indoors I generally have to raise the backlight higher than I would for other content, and that's a good chunk of the power draw so makes a dent.