Sometimes here at goodmama we find prints and fabrics in dark and luscious colors that are too gorgeous to pass up. I know we are talking about diapers here. They are things that get washed, and washed a lot.
The good general rule is to remember that diapers are laundry, just like everything else you wash. A new black, red or hot pink shirt will do best if it is washed separately in cold first. This cold wash sets the dye and eliminates many potential issues you may have otherwise. This same rule apples to diapers too.
It is true that you can use a goodmama fitted right out of the package, but they are actually designed to fit properly after several washes, and with bright and/or dark colors it is best to wash them in cold once before wearing. Often the pH of what goes into a diaper interacts with the unset dye in a brand-new diaper with unpredicatable results.
Another thing to be aware of, is our cotton/poly diapers may leave a fuzz on your baby the first time they wear it. This is not dye transfer, it's just little fibers left over from the shearing. If you wash your cotton/poly diapers once in cold before you ever use them, you will eliminate this fuzz and remove any possibility of dye transfer.
Many people have no problem with dye instability, but everyone's laundry routines, machines, detergent and water quality are different. Also remember, all prints eventually fade. If you had a t-shirt in one of the fabrics in our diapers, and washed it several times a week, you would expect to see fading. Diapers are, after all, clothes.
Some of our customers wash on cold, some line dry to keep the shells of the diapers out of the dryer. If you hang them in the sun, try to hang them so the print is not in the direct sunlight, unless you don't care about fading. I think a lot of faded prints look great; they have a Shabby Chic look to them. Your preferences may be different. :-)
In any case, remember: when in doubt, wash in cold first. And happy diapering!