continuous variable overlays switch from gradient to discrete when heavily subsetted

[danicahelb]

Data viz topic:

heavy subsetting switches the legend for a continuous variable from the gradient to the standard categorical colormap

See: GEMS1 scatterplot using BMI-for-age as overlay:

unsubsetted:

with heavy subsetting:

[danicahelb]

duplicates https://github.com/VEuPathDB/web-eda/issues/1583