Percentage vs transparency

[Ryan]

I've wondered for a long time, but is there an advantage/disadvantage to using a % of color (talking vector art here) vs using transparency? does it make a difference when it prints. I have a job that is going on fleece that will be using halftones of colors to minimize the colors and wondering about sepping it if I should change those to a transparent color over the base or if I should halftone the base but that would seem counter intuitive as the color would appear darker with a halftone base and color? does any of this make sense as to what I'm trying to figure out? here is the file. The red and brown are the colors i'm trying to figure out what to do.
thanks

[mk162]

I love to halftone the base and print solids on top of that.  I seem to be able to control it better.  I would omit the base in the darkest of each of the spot colors and let the gray hoodie darken it.  I am sure others would do it differently.

I did one yesterday where we printed a solid base and put halftones in the black and highlight white to make a nice gray.  It was going on white and a couple shades of gray, so we decided on a solid base and it did great.  SO you could print a solid base with the halftone color and use a halftone white to help prevent spread.  You would also get better halftones as they tend to mix pretty well on a solid base.

[zanegun08]

The main difference is a percentage of a color accounts for a white under base, and transparency is with no base.

In this example, the colors on the left are 50% fill, and the colors on the right are 50% transparency

They can print the same on press depending on how you setup your under base and artwork.

I prefer the transparency route, as if you stick colors underneath it effects the output more realistically on press, but it really just depends on how you setup your art, as to the rip the whole image will output a 50% black halftone across the image, the rip doesn't see a difference (unless colors are overlapping, and even then you can hit overprint and then the percentage is what you set the transparency.)