Alpha Channel?

[Zeno[IMMORTALS]]

Some units like the tsars gaurd have an extra texture wich I think is called an Alpha channel. I looks like the main texture but instead its all rainbowish. I can make my own texture for the unit but it doesn't look quite right unless I can make that alpha channel texture. I use photoshop so does anyone know how I can make that rainbowish texture so it will match my main texture?