Summary

Loosely insprired by #19479.

We have separate property cycles for lines and patches. This is a source of confusion and IMHO doesn't give a benefit.

Proposed fix

Unite the property cycles so that an Axes has just one cycle to draw from, no matter what the Artist is.

• Most simple plots use only either lines or patches. They wouldn't know the difference.
• If plots have both lines and patches, e.g. one line, one bar plot, IMHO it's more clear to by default use different colors.
• It's quite unlikely that people implicitly rely on synced colors to intentionally have parallelism between the lines and colors.

Migration:

• Add/document a way to get the state of the next element in the cycle (as long as there are two, use the line cycle). This will enable explicit use of a cycle element for multiple artists like this:

  prop = ax.prop_cycle_next()
  ax.plot(..., color=prop['color'])
  ax.bar(... color=prop['color'])
  

• Maybe consider ways to feed a cycle element back into a plotting function, either through an explicit kwarg ax.plot(..., prop=prop), or by ensuring that the cycle element can be dict-unpacked ax.plot(..., **prop).
• Minimal announce this as upcoming change in the release notes. If people are relying on parallel cycles they should move to the above pattern.
• We could also detect when both cyclers are used and issue a warning. The downside is that people will get a warning as soon as they use a mixture of lines and patches and they may be ok with the new behavior (it's unlikely they really intend to use the old behavior).