I don't know if their color is the same as WW2 field gray or not. I have German and British figures and no idea what to paint them. I also have only Tamiya and Model Master acrylic paints readily available for use.
"Sometimes things that are not true are included in Wikipedia. While at first glance that may appear like a very great problem for Wikipedia, in reality is it not. In fact, it's a good thing." - Wikipedia.
WWI fieldgrey and WW2 Fieldgrey are two different hues. the Germans tended to use tended to use a dark grey for everything. this all encompassing color is called Panzergrau or Tank Grey. WWI Fieldgrey is actually a myriad of hues ranging from very grey to very green. the common suggestion, is "Reseda Green" or the humbrol equivilant #31 Matte Slate Grey. YOu really can't go wrong with it. I paint all my troops and vehicles that way. some examples:
"General, you have nobly protected your forts. Keep your sword...to have crossed swords with you has been an honor, sir." General der Infantrie, Otto von Emmich
Ww1 and ww2 feldgrau is virtually indistinguishable, though it varied a lot from batch to batch. Ultimately you're looking at a dark greyish-green rather than a greenish-grey, imperial German trousers were often Steingrau (stone grey) (which in contrast to feldgrau, Is a greenish-grey)
The m1915 collar is a "reseda green" (Like steingrau but more green) except on Bavarian uniforms (they retained the plain feldgrau collar).
Remember, before 1917(citation needed), german leather is all a natural brown colour, before the kaiser ordered everything be oiled/polished black.
French uniforms were either a pale 'horizon' blue with bright red trousers, or later in the war, a greenish-brown khaki, similar to British and Soviet uniforms.
Hungarian I am fairly sure were a light kakhi but never having seen one in real life, I can't say for certain.