How do you change the color of your weapon camo?

I have a weapon camo I know can change colors but for the life of me I cannot remember how I made it red. Can anyone help?

That is done at the PSO2 Weapons Lab with the free service Change Photon Color, this service also works on compatible weapons and units too.

There are a few camos that don't need this like the Railgun from the Frame Arms Reloaded scratch, since it takes on the main color of your outfit/CAST parts.

Although there is a glitch where Photon Color can change to character default color in NGS.