The drawback of this representation of correlations is that the maximal luminance is not placed at the position of the (normalized) reference value (0 in this case).

To be more informative such a heatmap must have isoluminant and opposite colored cells corresponding to values $-a$ and $a$. In our image the cells corresponding to -0.19 and 0.19, for example, are both blue and of different luminance.

It would be also more informative that the luminance at left and right of the position of maximum luminance decrease monotonically with the same speed. In the image above -0.39 and 0.39 have opposite colors, but do not have the same luminance.

Our aim is to associate an asymmetric diverging colormap to an asymmetric data range with respect to a reference point, starting from a (symmetric) diverging colormap, considered as being associated to a symmetric interval of data values with center at the reference point.

Such a colormap will have the maximum luminance at the normalized reference point, and a decreasing luminance with the same speed toward ends, as in the images inserted in the next cells: