Changing the color of "walls" in Scatter 3D

I’m writing a DASH app related to PLS / PCA including some interesting 3D graphics.

The question is very easy:

I like dark colours for my apps and I’d like to change the “gray” colour of the “walls” (axis X,Y,Z) but I don’t know which attribute has to be used in the layout (probably).

Thank you in advance by your help.