Bottle brush is a great landscape plant, can't hardly go wrong.
For extra color intensity, things to think about would be more red, more purple, brilliant yellow which contrasts with both, or clear white, which contrasts with everything and would be nice against the dark green foliage of the bottle brush.
For more red, there's a desert plant called Fairy Duster, that is also evergreen and has red fluffy flower balls, gets 3' tall (you didn't say if your bottle brush is dwarf or not-- if it's full size, the 3' tall would be good height with it).
For yellow, there's yellow bells, again evergreen and hummingbird attracting. Gets pretty big, but you can keep it pruned to whatever size you want.
For purple there's Texas sage (also called purple sage). It's an evergreen salvia that gets covered in purple flowers.
For white, Shasta daisies might be a good choice, brilliant white daisies that keep coming all season.
Or there are lupines which come in a variety of colors. native plant, attractive to birds and butterflies, naturalizes well, attractive foliage.
Look them up, see what you think.. I'm sure other people will have lots of other good suggestions.