From the description:
The Extra Team Colors pack basically includes an alternative skin with different colors for each and every default commando and soldier skin. The alternative colors are black, purple, cyan, teal, and orange (Although, there are some skins that already black/cyan colors such as the Necris, Aphex and female War Machine, so they'll have white and blue colors instead).
This does not actually add more teams, so I wouldn't recommend using it for Team Deathmatch or Capture the Flag unless you don't mind having a guy wearing purple on your red team. This was made mostly for non-team-based matches for those who want to have more color options.
To install this, just put the files in the zip in their respective folders, which can be found immediately inside the Unreal Tournament folder. Int files go inside the System folder, and UTX files go inside the Textures folder.
Credit goes to Shane Caudle and the other artists at Epic Games that worked on UT99 for the original textures. I extracted said textures from the game with UnrealEd and edited them with Photoshop and GIMP.
Later on, I may make a v2 of this that includes alternative colors for the characters in the bonus packs. I may change the colors up a bit too if enough people are bothered by my selection of colors.