How the black prints using a white toner printer

The black is produced with the cyan, magenta and yellow toners.

On a normal CMYK printer the black is produced using the K toner predominantly. Which then produces a true black.

The OKI white toner printers use CMYW toners, they do not have a K toner. This means that the black they produce is from the CMY toners layering on top of each other. This is known as composite black. It may have a greenish tinge to it, but this is unnoticeable unless printing black onto a black t-shirt.

Forever have black Flex-Soft paper for this specific conundrum, which allows for a true black to be produced on a black t-shirt.