To improve the display for the project, I ordered a set of 5mm NeoPixels from Adafruit. They arrived quickly and have replaced the original blue LEDs on the protoboard. The NeoPixels will give capability for better control over the hue of the display, and several LED's can be controlled with fewer pins on the Trinket., reducing the rat's nest of wiring that often accompanies LED displays. So far, the biggest problem with using NeoPixels has been locating a schematic for them. The Adafruit NeoPixel Uberguide fails to provide a pinout for the 5mm version. Finally, I found a schematic lurking in the middle of a new product video.
The display will allow information to be conveyed by using a variety of colors as cues. Currently, the plan is to start with a "brighter" color when the breath pacer is first turned on -- probably a shade of yellow. This will indicates to the user that his/her breathing rate is not yet optimal. As the pace is slowed, the display color will move toward green and finally end on blue, indicating that the optimal breath frequency has been reached. At the same time, different LED's in the display will also be activated to indicate inhalation and exhalation.