Slitherine

The game doesn't seem to understand the need to map using the Four Colour Theorem (https://en.wikipedia.org/wiki/Four_color_theorem). Massilia, Arverni and Galli are all the same colour of brown in my current game when the political view is chosen making the political view useless.

In this attached example, the Arverni have just become Massilia clients. Up until then they were the same colour as Galli and Massilia.

Four Colour theorem applied to the game would mean nations would change colours constantly, which is not something desirable. I do agree that some work could be done on the current colouring though...

Also, that theorem is valid for contiguous regions.
In this game, countries are often not connex at all. It's common to have a bit of Carthage here and there on the map, not connected to the rest.
Thus, the theorem cannot apply to this game.
But yes, there should be options to customise at least some country colors in order to be able to distinguish neighbours.

Really, be my guest

You'll see that this is not obvious to find better coloring for nations, if you take into consideration:
a) possible areas of expansions
b) new nations emerging in the vicinity
c) that colors are not opaque but translucid (so 2 colors that should be different ends up too close chromatically speaking)
d) some nations had an "historical" color associated to them (Rome & red, etc.)

A solution to the color problem is to allow the player to change the hue of their own nation and mayeb of any other nation, using a color selector. That way if I want to have Pontus appear blue because I'm Athens and we're both white but we share a border (as Dacia I always have a brown neighbour, etc.), I could do it.
Another option is to add borders of a different color to the shader, so for example the inner color of the province is white but the border is grey or red... that way each nation is defined by a core (center) color and a border color, which means you have much more space for making them unique.