Hi Steven. All shirts fade very slightly when first washed, but with most types of garment decoration, you would struggle to see any difference.
Take a 50/50 poly cotton shirt though, printed up with sublimation inks and it will look OK when sold, but you'll end up with a very annoyed customer when it gets put through its first wash cycle. You'll end up with a significantly faded look to the garment.
50/50 poly cotton fabrics really aren't worth all the hassles you'll inevitably get, for a small saving on price.