The game supports CGA and EGA but for some reason it only runs in CGA mode.
The EGA Version looks much better as can be seen here on MobyGames.
Is there any command line option not mentioned in the documentation to run in EGA mode?

In the game's page on Giant Bomb those same screenshots are also there, but the EGA ones seem to be from the Atari ST version.

https://www.giantbomb.com/firezone/3030-25379/images/

I don't personally have this game, but I assume you checked the following?


Is there a .exe in the game directory for installing. e.g. install, setup

Editing the gog supplied dosbox .conf file and setting machine=ega

As a last resort, could also update the Dosbox to a version supporting cga composite like Staging and see if the game supports that mode.
machine=cga, F12 to enable, Ctrl+Alt+F11 to cycle.

The Atari ST images on Giant Bomb really look like the DOS EGA images on Mobygames especially because of the colors. Atari ST and EGA 320x200x16 graphics are hard to distinguish because both have 16 colors and the graphic is often identical. You have to look closely on the pallette to see differences in the colors in screenshots. There is no extra executable with the exception of the scenario editor.

Setting the game to ega did not help.

There are several files ending with .cga. I took a look into the exe files and the .cga files are all referenced there. But there are no references to .ega files. Maybe there was no ega version or the game had an own exe file for the ega version.

P.S.
I was blind, there is a file called fz_ega.dat that is not referenced in any other file. Now it really looks like there must be an ega version.

Some game exes have command line parameters, often the graphic modes are changed using something like "e" or "ega" "/e"
Does the game come with a manual?

btw,
"machine=ega"
in the config file does not change the game, but configures the hardware emulation of the virtual machine used for dosbox.

Usually "svga_s3" is the best option, since ist supports svga, vga, ega and cga rgb emulation. You only change that if you have a game with tandy graphics or a game that supports cga-composite (and only if your dosbox version supports cga-composite in the first place, the default 0.7.4 version doesn't).

Thank you for your answers. I took a look at the Atari ST Version and it contains nearly the same files as the GOG DOS version but the CGA files are replaced with EGA files. I assume the DOS version was first and because of the similar graphic mode on the Atari ST they took the EGA files.

I couldn't find a parameter that enables EGA graphic in the GOG DOS version. This cannot work because the EGA files are not included and, more important, they are not referenced in the executable. Only the CGA files are referenced. This explains all. An EGA executable that is referencing the same EGA files that the Atari ST Version. Thank you.