diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -6586,8 +6586,6 @@ def hist(self, x, bins=None, range=None, density=False, weights=None,
         if histtype == 'barstacked' and not stacked:
             stacked = True
 
-        # basic input validation
-        input_empty = np.size(x) == 0
         # Massage 'x' for processing.
         x = cbook._reshape_2D(x, 'x')
         nx = len(x)  # number of datasets
@@ -6649,13 +6647,10 @@ def hist(self, x, bins=None, range=None, density=False, weights=None,
         # If bins are not specified either explicitly or via range,
         # we need to figure out the range required for all datasets,
         # and supply that to np.histogram.
-        if not input_empty and len(x) > 1:
-            if weights is not None:
-                _w = np.concatenate(w)
-            else:
-                _w = None
-            bins = np.histogram_bin_edges(
-                np.concatenate(x), bins, bin_range, _w)
+        all_xs = np.concatenate(x)
+        if len(all_xs):
+            all_ws = np.concatenate(w) if weights is not None else None
+            bins = np.histogram_bin_edges(all_xs, bins, bin_range, all_ws)
         else:
             hist_kwargs['range'] = bin_range
 

diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
@@ -68,6 +68,7 @@
 from collections.abc import Sized
 import functools
 import itertools
+from numbers import Number
 import re
 
 import numpy as np
@@ -260,14 +261,12 @@ def _to_rgba_no_colorcycle(c, alpha=None):
             return c, c, c, alpha if alpha is not None else 1.
         raise ValueError(f"Invalid RGBA argument: {orig_c!r}")
     # tuple color.
-    c = np.array(c)
-    if not np.can_cast(c.dtype, float, "same_kind") or c.ndim != 1:
-        # Test the dtype explicitly as `map(float, ...)`, `np.array(...,
-        # float)` and `np.array(...).astype(float)` all convert "0.5" to 0.5.
-        # Test dimensionality to reject single floats.
+    if not np.iterable(c) or not all(isinstance(x, Number) for x in c):
+        # Checks that don't work: `map(float, ...)`, `np.array(..., float)` and
+        # `np.array(...).astype(float)` would all convert "0.5" to 0.5.
         raise ValueError(f"Invalid RGBA argument: {orig_c!r}")
     # Return a tuple to prevent the cached value from being modified.
-    c = tuple(c.astype(float))
+    c = tuple(map(float, c))
     if len(c) not in [3, 4]:
         raise ValueError("RGBA sequence should have length 3 or 4")
     if len(c) == 3 and alpha is None:

diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -604,7 +604,9 @@ def test_shaped_data():
     plt.plot(y2)
 
     plt.subplot(413)
-    with pytest.raises(ValueError):
+    # DeprecationWarning is raised by numpy 1.19 on object array creation;
+    # later it will be a ValueError again.
+    with pytest.raises((ValueError, DeprecationWarning)):
         plt.plot((y1, y2))
 
     plt.subplot(414)
@@ -2697,7 +2699,9 @@ def test_boxplot_bad_ci_2():
     x = np.linspace(-7, 7, 140)
     x = np.hstack([-25, x, 25])
     fig, ax = plt.subplots()
-    with pytest.raises(ValueError):
+    # DeprecationWarning is raised by numpy 1.19 on object array creation;
+    # later it will be a ValueError again.
+    with pytest.raises((ValueError, DeprecationWarning)):
         ax.boxplot([x, x], conf_intervals=[[1, 2], [1]])