Originally posted by @ImportanceOfBeingErnest in #12431 (comment)

I wonder if this is the correct fix. The documentation also states

c : color, sequence, or sequence of color, optional, default: 'b'
The marker color. Possible values:

• A single color format string.
• A sequence of color specifications of length n.

So for

plt.scatter([0,1],[2,3],c=("0.5", "0.7"))

one would expect two points with different shades of grey. But this is converted to an array of values and shown with the viridis colormap.
Not sure if the documentation is wrong here or the code.