Why are the colors in my gobo slightly different from what I saw on the web, PDF or printed copy?

When the gobo is printed on glass vs. paper

The medium the design is printed on has an effect on color. There are many types of paper but all paper is porous and will absorb some ink. Printing on a gloss paper vs. an uncoated paper will change the color. Glass does not absorb ink and the translucent nature of glass has an impact on the color.