Hovering avg/max speed in the stats panel switches the track from the
default gradient to a blue→green→yellow→red speed gradient. Progress
along the track is computed from cumulative distance (speed × time) so
fast sections appear proportionally long rather than time-weighted.
Reverts to default on mouse-leave. No-op when timeseries has no speed
data or the activity has no GPS track.
Davide Scaini
f71fe2ddf5