On the A-H map I would adjust the placement of some of the country labels that are partially covered or crowded by the A-H boundary. It seems odd to me that a map labeled "Austo-Hungarian Empire 1913" has modern day countries... I guess the intent is to show the extent of A-H superimposed on modern day countries. Could that be made clearer (without making the title too wordy)?
As for 4 colors see wikipedia - 4 color theorem.
The map has now served its purpose (as a slide in a powerpoint presentation), but I will bear what you say in mind for future reference! the intent was to show the extent of the AH empire against modern borders - most of the people at the conference (held in Vienna) were not Europeans and may not have been familiar with the poiltical geography of Europe in 1913. Thank you also for the 4 colour theroem which I will read with interest.
Just by way of a quick diversion, one of the most amazing co-incidences happened to me while I was drawing this map. I was at the local community rubbish tip / recycling centre throwing out some household waste. There is one area for 'general waste' which is just a huge pile of anything that people throw on it. Sticking out by my foot I saw the corner of a piece of paper saying 'Austria Hungry'. I pulled it out and found a perfect Bartholemew map of the AH empire pdf attached below and another one of Glasgow in the same period. I'm just so glad that the person who threw it away didn't put it into the paper recycling section!