Conventional Thermal dye transfer printing uses cyan, magenta and yellow (CMY) dyes to build up a full color image. This paper concerns the use of fluorescent dyes to build up a full color image which is virtually invisible under normal illumination, but glows brightly when illuminated with a UV blacklight. In order to obtain the image, the CMY dyeset is replaced by a red, green and blue (RGB) fluorescent dyeset. Unlike other forms of printing, the process employs additive color combination. If the RGB ribbon is used in a conventional printer instead of a CMY ribbon, the image must first be converted to a negative in order to give the correct color values. There are a number of applications envisaged for this process. It can provide an additional level of security on transaction cards, or it could be used for novelty applications.