First, I'd like to say I really like having the ability to map stats to line colors on the interactive map. Strava only applies this to the static images on the activity feed :|
However I'm finding that for cycling activities the HR on maps is crushed into a small part of the color scale; mostly all orange or red and zero blue is shown.
I think most people operate in a range of just 30-40 bpm (tops between cruising and all out effort max HR), and perhaps a much larger range is mapped to the color scale?
IMHO this should at least map the minimum and maximum during the activity to the scale. Perhaps a log scale would make sense to focus on the upper 30-40 range.