Matplotlib Color Gradient Based on Y-Value

I would like to plot a "cut" through a heat map, i.e. apply a color gradient to my plt.plot(x,y) based on the y-values (which are in a range of -0.5,0.5.

Any suggestions? I tried to workaround by using a scatter-plot, but the colormap seemed to be applied to each line individually (and not globally).

Thanks!

EDIT To describe it in other terms: I would like to map each y-value in the interval to an appropriate color in my colormap. (The phrase 'cut through heat map' just refers to the commonly used technique to map the z-values of a function z=f(x,y) for given x and y to a color.)

As mentioned earlier already, just applying a colormap to a scatter-plot seems to to map the maximum y-value of each line (as i am plotting multiple series) to white, as seen in the attachment. Instead, I would like to map the global y=0.5 in my plot to white and -0.5 to black for each line.