# After this block, c_array will be None unless
        # c is an array for mapping.  The potential ambiguity
        # with a sequence of 3 or 4 numbers is resolved in
        # favor of mapping, not rgb or rgba.
        if c_none or co is not None:
            c_array = None
        else:
            try:
                c_array = np.asanyarray(c, dtype=float)
                if c_array.size == x.size: # <<- here is the interesting line.
                    c = np.ma.ravel(c_array)
                else:
                    # Wrong size; it must not be intended for mapping.
                    c_array = None
            except ValueError:
                # Failed to make a floating-point array; c must be color specs.
                c_array = None

        if c_array is None:
            colors = c     # must be acceptable as PathCollection facecolors
        else:
            colors = None  # use cmap, norm after collection is created

import numpy as np
import matplotlib.pyplot as plt
x = np.arange(4)
y = np.arange(4)
colors = np.random.rand(2, 2)

fig, ax = plt.subplots()
ax.scatter(x, y, c=colors)
plt.show()