The Rainbow-technology is based on a pretreated, high-grade cotton yarn, which dyes much deeper than regular, untreated cotton. Due to the different dyeing properties, patterns woven or knitted into the raw fabric can be made visible in the desired color after piece dyeing. Various levels of color intensities can be achieved by using a combination of Rainbow yarns with different levels of the Rainbow-treatment. The dyeing process can be controlled in a way that a pattern appears «color on white» or «tone on tone» (different color intensities). By blending Rainbow-treated fiber with regular, untreated cotton, a heather-yarn in Rainbow-technology can be produced. After piece- or garment dyeing, the heather effect becomes visible in any desired color. The advantages are obvious: full flexibility in color selection, short lead-times, no minimums for special colors, no surplus inventory of heather-yarn, etc.