Add a label to the barrel as an image texture. A. Have the diffuse dot whetever color you want the barrel before you click it over to the "A" channel. In your case, grey. B.Make sure you make that Alpha image of the label. Just a inverse of your label texture. C. Choose Decal colors, this will apply the label on the colored barrel and using the alpha channel, make those areas that are not the logo on the label to be transparent.

Contact Me | Gallery | Freestuff | IMDB Credits | Personal Site
"I want to be what I was when I wanted to be what I am now"