What I see there is the full range of colors available, grouped into gradients (more or less)
As I understand it, each pixel has a "daylight color" and a "night color" (the start and end of a specific gradient) and a twilight pixels' color is calculated depending on the position in the twilight, and then, the appropriate color from the palette (in between those pixels) is used.
Did I get i right?
So, by using this algorithm, the original Xcom created those"bands" of shading, because only that set of colors were available.
Then... this sucks
Anyway, any plans on increasing the depth? After 1.0 I mean. I'm pretty sure that there will be quite a lot of people out there who would like to give Xcom a facelift. Higher resolution/redone graphics and maybe audio. That would require a 24/32 bit depth.