I have bought Empire Earth I: Gold because it is said that the game is working on Windows 8.1. However whenever I open the menu, the graphics are weird and even if I'm able to start the game, the graphics and colors are totally mixed. I'm unable to play the game. I've tried regedit changes. They weren't any help either.

http://easywinclan.forummotion.com/t1707-ee1-empire-earth-and-empire-earth-the-art-of-conquest-windows-8-81-fix

Since you have got the NVIDIA graphics card, try the SOLUTION 2.

I have windows 8.1 and a double chipset (nVidia GTX850M and Intel HD4600) and tried every solution in that post above with no results. Has anyone found another fix for this issue?

Could you install a program called: MSI Afterburner, and then enable On-Screen Display in settings? (tutorial)

I have noticed that when a game is using the integrated GPU (Intel HD), then the font of OSD is black, and when the game is using a normal GPU (Nvidia), then the font is pink. So if the font is black for you all the time, it means that NVIDIA graphics card doesn't work in EE1, and this problem should be reported to the NVIDIA support.
We had a similar problem with Empire Earth II, but it has been fixed after my intervention (details)

I tried yesterday with the MSI afterburner but couldn't get it to work, I got repeated error messages from the Riva Tuner Statistic Server, and no OSD whatsoever showed ingame. I will try again today and I'll let you know.

Please remember to install the Riva Tuner Server (it should ask you at the end of the MSI Afterburner installation). Also run MSI Afterburner as an administrator

I did install the RTS because it prompted me to do it, but I think I might had forgotten to run it as an admin. I'll try again today, thanks for the hint ;)

Well I tried again today, installed MSI with admin permissions and this time there was no issues and the OSD showed in pink letters in several games I tested it on (Neverwinter Nights and AoW 3), but there was no OSD showing in EE or AoC, pink or otherwise :/

Thanks anyway for your suggestion.

When you minimize MSI Afterburner, two icons will be visible in the system tray (notification area, right-bottom corner, next to the clock). Click on the RivaTuner Statistics Server icon and change in "Global" Application profile properties -> Application detection level to "High". Then it should also detect Empire Earth 1.

Ok thanks, will check it out later ;)

Ok, finally got it to work, and the OSD shows in game in pink letters, so I guess it's the nVidia GPU the one that's running the game. Also in 'GPU usage', the number in GPU1 (nVidia) is much higher than GPU2 (IntelHD).

Okay, then you can try to install older NVIDIa drivers and see how it works (for example this one: http://www.nvidia.com/download/driverResults.aspx/74636/en-us ).

No luck :/

With those older drivers the problem remains the same; I also tried solutions 2 and 3 from your other post above after installing the older drivers, with no success: solution 2 does nothing and when trying to access 'Game settings' for sol. 3, the game completely freezes.