Question

simply, given an initial color “#1010CA” and an alpha factor 0.5, how can I get the final color that is shown on the plot in terms of color="#1010CA", alpha=0.5?

or more straightforwardly, what should I fill in

plot(x, y, color=__)

so that it is equivalent (at least visually) to

plot(x, y, color="#1010CA", alpha=0.5)

? I guess it shouldn’t be a python question, instead how to manipulate the rgb colors by some factor to damp it, but forgive my ignorance in color palettes…

EDIT

Here is the current solution I opt for after taking @Blender’s answer

import matplotlib
import numpy as np
def alpha_blending(hex_color, alpha) :
    """ alpha blending as if on the white background.
    """
    foreground_tuple  = matplotlib.colors.hex2color(hex_color)
    foreground_arr = np.array(foreground_tuple)
    final = tuple( (1. -  alpha) + foreground_arr*alpha )
    return(final)

Answer 1

You can’t get a “final color” without the background color as well.

But for rendering alpha transparency, I would guess that a weighted sum would work:

final = (1 - alpha) * background + alpha * foreground

So if your color is white and your alpha = 0.5, you can do:

final = rgb(0.5, 0.5, 0.5) + foreground / 2

Matplotlib accepts RGB tuples so you can make an opacity flattening function pretty easily. Why you need to do this, however, is not something I can answer.