Really well done, but I agree with one of the comments in there: need to add patterns to the solid colors; it would differentiate for color blind folks and in general make the relationships easier to grasp.
The inner join is already perfectly distinguishable by how dark the squares are, and anything other than monochromacy preserves the distinctions that the color adds in the cross join, unless the site I used is misleading.
[1] https://www.color-blindness.com/coblis-color-blindness-simul...