[jerlam]

Apple used to reserve the "mature" muted colors for the Pro, and the colorful ones for the base model. Not only did they switch the schemes this year, the Pros also have one less option which suggests... something.

[hbn]

I'm pretty sure at least in the last 2 years they were kinda limited in colors they could do because titanium is difficult to inject with color.

Before that they used stainless steel, I think they wanted to differentiate the frame from the non-Pro lineup to seem more "premium"

But this year I guess they finally gave in and just use aluminum on the Pros and now they're free to color however they want.

[layer8]

Margins on the Air are probably higher than on the Pro, at least for the base storage models, so they may be trying to nudge people to the Air.