If I understand the API correctly, I should be able to turn the backlight on to the current system brightness level using
Attention.backlight(true);
Running in the simulator, I see the backlight change from Off to Default but on a real device (Epix 2), the backlight does not actually turn on.
If I use the alternate syntax and set a float value (between 0 and 1.0) for the backlight, everything works as expected.