closes #16593 setting ecolor turns off color cycling

Co-authored-by: tacaswell <tcaswell@gmail.com>

lib/matplotlib/axes/_axes.py

@@ -3215,8 +3215,7 @@ def errorbar(self, x, y, yerr=None, xerr=None,
             # Remove alpha=0 color that _process_plot_format returns
             fmt_style_kwargs.pop('color')
 
-        if ('color' in kwargs or 'color' in fmt_style_kwargs or
-                ecolor is not None):
+        if ('color' in kwargs or 'color' in fmt_style_kwargs):
             base_style = {}
             if 'color' in kwargs:
                 base_style['color'] = kwargs.pop('color')
@@ -3227,6 +3226,7 @@ def errorbar(self, x, y, yerr=None, xerr=None,
         base_style.update(fmt_style_kwargs)
         if 'color' not in base_style:
             base_style['color'] = 'C0'
+            color = 'C0'
         if ecolor is None:
             ecolor = base_style['color']
         # make sure all the args are iterable; use lists not arrays to

lib/matplotlib/tests/test_axes.py

@@ -3266,7 +3266,21 @@ def test_errorbar_offsets(fig_test, fig_ref):
         ax_ref.errorbar(x[shift::4], y[shift::4], yerr[shift::4],
                         capsize=4, c=color, fmt='none')
 
-
+@check_figures_equal()
+def test_errorbar_ecolor_cycle(fig_test, fig_ref):
+    x = np.arange(0.1, 4, 0.5)
+    y = [np.exp(-x+n) for n in range(4)]
+
+    axt = fig_test.subplots()
+    for yi in y:    
+         axt.errorbar(x, yi, yerr= yi*0.25 , linestyle='-', 
+                        marker='o', ecolor='black')
+
+    axr = fig_ref.subplots()
+    for yi, color in zip(y, ['C0', 'C1', 'C2', 'C3']):
+         axr.errorbar(x, yi, yerr= yi*0.25, linestyle='-', 
+                        marker='o', color=color, ecolor='black')
+
 @image_comparison(['hist_stacked_stepfilled', 'hist_stacked_stepfilled'])
 def test_hist_stacked_stepfilled():
     # make some data