> the grid itself is perceptually more or less uniform
I can tell you that the grid is more physically uniform than perceptually uniform. It is well known that humans are physiologically less capable of distinguishing hues of blue than of most other broad categories. This property is encoded in most colorimetric systems, such as CIEDE 2000.
Update: I read a paper some years ago which I can no longer find an English copy of[0]. The author used Isomap to project the mutual perceptual distances (as modeled by CIEDE 2000) of physically-uniform colors onto a two and three dimensional euclidean space, with very interesting results (toward the end of the PDF).