The adagio doesn't seem that dark. I don't think there will be much of a contrast between the two..As for in or out as a trend, it doesn't matter..if you like it, go for it

I agree with printesa, Adagio is not too dark a color. If you prefer lighter colors like Sterling in your bedroom, then going with Adagio as an accent wall color could work well.

I personally wouldn't do an accent wall of paint. If I wanted to highlight something, I would do it another way. In this case, in a master bedroom, I would only highlight the wall that the headboard is on, and I would do it with a subtle patterned or a textured wallpaper as you mentioned or with a wall of drapery panels or mirrors or art or (most likely) some combination of those. If you want to highlight a wall, then highlight a wall ... I think paint is not going to give much of an impact.