They all have wrong colors when I play anything in full screen in DOS, the left side of the screen is cut off slightly so I can't see text properly.

Is there a way to fix this or resize the window to fit the screen without being full screen?

That shouldn't be happening. You may want to try adjusting in the ini file the aspect ratio and color machine - relevant terms are fullresolution (or windowresolution for windowed mode) and machine (hercules,cga,tandy,pcjr,vga). The ini file should be in the game folder with a name like dosboxpref.conf or dosboxini.conf or something like that and there may be a master config file with your dosbox install too (though changes to the game specific one should override that).

I would make sure the .conf for the game says these:

fullresolution=original
windowresolution=original
machine=svga_s3
memsize=16 (memsize = 32 can apparently also screw things up)

Assuming we are talking about a DOSBox iusse here, you could try to change the "output=" field to something different (you can choose among "surface", "overlay", "opengl", "openglnb" and "ddraw").

Seems like dosbox is not reading its configuration file.

Check if you did not accidentally change the file dosbox <insert game name>.conf to dosbox<insert game name>.conf.txt

If the extension is not .conf then it will not load.

I really need to manually configure EVERY DOS GAME I OWN? Thanks, but I don't have either of those files.
Would reinstalling dosbox fix it?

Lets get some background.

Are you refering to just Dosbox games purchased on GOG?

Have you ever manually installed Dosbox on this system?

Have you changed any Dosbox configurations while trying to get a non-GOG game to work?

Do the games install and work properly on another system?

What games specifically are you having issues with?

I just noticed I'm also getting this pop up.
Changing anything doesn't help though. Do you know how to fix that for games that don't use Dosbox, like starcraft?

Try this. I just linked a previous post I made in an earlier thread dealing with a similar problem to avoid retyping. Hope this helps.

No it is not necessary unless you are having problems with a game or you simply want to tweak some settings. For example: the game is running too slow, speech is being cut-off.

Games that you purchased on GOG that use DOSBox usually work right out of the "box". You don´t really need to do anything.
The game installer automatically installs a DOSBox version along with the game files.
In the game directory there will be a file called dosbox<insert game>.conf

For example the game Teenagent installs a DOSBox version 0.72 in its directory.
On my PC the path is F:\GAMES\GOG\Teenagent.
There is a a DOSBox configuration file named dosboxTeenagent.conf that i can edit using notepad if i wish.

Tyrian 2000 also installs a DOSBox version (in this case 0.74) in its directory and there is configuration file named dosboxT2K.conf

In other words, you can have many DOSBox versions for each GOG game installed on your system. And when you run the game, it will use the DOSBox in its directory.
Not the DOSBox that you might have downloaded and installed of the Internet.

That fix worked on the psychedelic colors for Red Baron 3D for me, but I'm not sure it would apply to DosBox games. Worth a shot.

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@BananaJane

GOG games should work out of the box. For other non-GOG DOS games I would recommend a front-end (in OSX I use Boxer) to simplify your life.