This is just a re-skin of the liquid in a bottle of mad milk, the impact splash, and the resulting drops on an enemy player.

You have two choices. normal sized drops or large squares.
The color choices are. red, blue, green, pink, orange, and rainbow

The rainbow color changes between the different colors of the rainbow. The rainbow color only changes the liquid in the bottle.

the splash, impact and icon are still white. I cannot figure out how to make the colors change.

I have changed the mad milk icon to match the color. the icon has a slight distortion. gimp caused the distortion when I exported the file.

I may add more color if requested to do so.

To install. choose what color and sized drops you want. only choose one of the folders. the folder either has normal sized drops

or large square drops based on the name of the folder.
SteamApps/common/Team Fortress 2/tf/custom