Hi Steve - it's because each of those grids are defining a local coordinate system.

So the blue lines you see there on each grid are showing the y axis of each grid's coordinate system, not the world coordinate system.

Having it set up with a locally defined system like that is kind of more in line with allowing those planes to be individually re-oriented to a custom direction that is not necessarily aligned to the world axes like they are by default.

But I've also been thinking of not allowing to just set one viewport's plane individually (except maybe the 3D view) and instead having just one plane in common for the Top/Front/Right views. That kind of organization would make it more feasible to have the colors as you had expected.

Right now you are seeing the result of a more generic "each view has its own 2D drawing plane" type system.

- Michael