Hair Coloring 130 Table 3 Dye reaction products Primary Intermediate Coupler Dye Color NH 2 NH 2 HO NH 2 H 2 N N O H 2 N H N NH 2 Brown NH2 OH HO NH 2 H3C N CH 3 HO O H 2 N Orange N(CH2CH2OH)2 NH2 OH N (HOH2CH2C)2N O Blue Any new dye added to the palette requires significant safety data before it is approved for use, and this safety testing is expensive. As a consequence the number of new commercial dyes that have been introduced over the last ten to fifteen years is very small, even though the patent activity on new dyes has been significant during this time. The new dye precursors that have been added to the dye palette primarily target new shade areas such as reds, yellows, oranges and blues to enable the brighter, vibrant shades.16 A number of the new dye precursors are based on heterocyclic structures which can form these pure colors that are stable and relatively wash resistant. The advantage of these structures is that the dyes form much smaller chromophores and thus much more vibrant colors. The 1-hydroxyethyl-4,5-diamino pyrazole sulfate(below, left) forms very vibrant red shades with couplers such as 2-methyl-5-aminophenol, and 2,3-diamino-6,7-dihydro-1H, 5H-pyrazolo[1,2]pyrazol-1-one (below, right) forms an orange red with the same coupler.