I came here to ask the same question about the regen bar in my 2018 M3. Even after I read this thread, I didn't notice it until I put the screen in the dark mode, then it was clear. Then I could notice it even not in the dark mode, but is very difficult to see. Not real important anyway.
FWIW, I like the way it is done in my 2022 Chevy Bolt MUCH better. It shows the loss and gain in KW. I wish Tesla would do that. And the Bolt has progressive regen from the brake pedal. I doubt if the brake pads ever even engaged on that car. Brake harder, get more regen. I normally just use the regen level on the steering wheel to stop as it cannot engage the brake at all. Another nice feature I wish my Tesla had.
IMAO, conventional brakes are no more than a big waste of good energy.
-Don- Reno, NV