code: def test_plt_longterm_ts_agg_fixed_color():
      """Testing `plt_longterm_ts_agg` with fixed color across"""
      r = 10.0
      x = np.linspace(2.0, 2.0 + r, num=100)
      y = np.linspace(3.0, 3.0 + r, num=100) ** 2 + np.random.normal(
          0, 20, 100
      )
  
      df = pd.DataFrame({"x": x, "y": y})
      df["window"] = df["x"].map(round)
  
      plt_longterm_ts_agg(
          df=df,
          time_col="x",
          window_col="window",
          value_col="y",
          agg_func=np.nanmean,
          plt_title="fixed color",
          color="blue",
      )
  
file_path: greykite/greykite/tests/common/viz/test_timeseries_plotting_mpl.py
imports: import datetime
  import math
  from functools import partial
  import matplotlib
  import numpy
  import pandas
  import scipy.stats
  from greykite.common.viz.timeseries_plotting_mpl import plt_compare_timeseries
  from greykite.common.viz.timeseries_plotting_mpl import plt_longterm_ts_agg
  from greykite.common.viz.timeseries_plotting_mpl import plt_overlay_long_df
  from greykite.common.viz.timeseries_plotting_mpl import plt_overlay_with_bands
label_desc: Use image node_id 4 for calling a global function with example usage: test_plt_longterm_ts_agg_fixed_color() without return types