Yes.
I don't have much experience with making custom maps from scratch, but I do believe that the province.png map should have the same format as the original vanilla map. But I sense there might be even larger problem why things don't work for you:
I'm not sure what you mean.
Do you know that the provinces should have the exact colors, as defined in the definition.csv file, right?
The values in that file mean
province ID;Red color value;Green color value;Blue color value;Province tag; etc.
Also in the province.png, you should only use colors, which are defined in that definition.csv file. If you want your game to load properly, you should list all provinces there and use the colors for those provinces, as they are defined in that file.
If the color on your province.png doesn't reflect the values in your definition.csv, the game won't load those provinces.