So I got bored and did an item-by-item check:
General: A lot of colours have a base that is either very light or very dark. This creates readibility issues with the lighter/darker shades, as they become less distinguishable from teh base colour when extremes of luminosity are used ffor the base colour. You're not the only one to make this mistake.
Carolingian Empire vs. Franks: These are basically the same thing (one is the name of the most notable Frankish dynasty; the other is the name of the culture-group ruled by that dynasty; it is historically correct to call the Carolingian Empire a late development the Kingdom of the Franks).
You have Western Roman Empire and Gallic Empire under the same colour. While they didn't exist simultaneously (11 years separate them), it does imply a strong relationship between them which doesn't exiost OTL (one was a planned division of power; the other was an open rebellion). A simular issue exist with the colour for Eastern Roman Empire/Palmyrene Empire.
Prussia/Teutons: "Teutons" were a Germanic tribe that lived in northern Denmark. If you mean Teutonic Knights, say so. The two are not the same.
Szekerland: These guys are mostly ethnic Hungarians in modern Romania, not ethnic Germans (the biggest concentrations of Germans in Romania are in the northwest and west border regions, not Szekelyand)). For a Germanic state in eastern Europe, the most notable example is the Volga German ASSR (which you have listed separately). no reason not to have a "Germans in SE Europe e.g. Szekely" colour of course, but a "Hungarian Szekely" colour is needed.
Nonary German state: The "Congo joke" got transferred to Germany, I see.
Congress Poland: As others have noted, this was really a Russian puppet, not an independent country. Maybe use this colour for the Free City of Cracow (1815-46) instead?
"other" Poles: Calling Polabians and Kashubians "Poles" is about as correct as calling Canadians "Americans", and I suspect, as likely to get a friendly reaction as calling a Scottish person "English".
Scythia: These guys were ethnic Iranians, a subset of the Indo-European you labelled them as. Ditto for the Sarmatians. It's about as correct as saying "nonary European state" instead of "nonary German state".
Finno-Volgaics: This is a discredited linguistic theory, not an actual OTL thing. Could still be an ATL thing of course, but it feels like giving undue notability. This and the other Finno-Gric colours could be useful for depicting the ethnic Hungarian migratory patterns though.
Why is ancient Macedon and Alexander's Empire separate? I'm fairly sure they were the same thing, except that one was rajing.
Tunesia (sic): spelling
Turkey: The problem with labelling separate colours for Islamist Turkey and Kemalist/secular Turkey is that there is a strong continuity of nationhood from Kamal himself through to the present near-theocratic regime.
Not sure why North Yemen gets to be the 4th option for a Yemeni country rather than the 2nd.
You have a non-socialist Venezuela, but no colour for a socialist Venezuela.
The states that declared (short-lived) independence from Brazil really ought to have colours.