Unable to change color scheme of plot_schedule_airmass

Hi all,
Because I'm dealing with many different objects at our observatory (~50/night), the current colormap used in the plot_schedule_airmass can be very confusing. I'm wondering if it's possible to change that colormap (since plot_schedule_airmass only takes a few parameters, none of which deal with the colormap). Thank you!

Start at the plot_schedule_airmass entry point and inspect how its current colormap is selected. Check the existing tests around this plotting function, then determine how a caller could configure the colormap without breaking current parameters. Done means the plot's colormap can be changed by the caller and existing behavior remains supported.

Written by the indexing model from the issue text.