Indole color former

A pressure-sensitive carbonless duplicating system or thermal marking system containing a support sheet coated with a color-forming substance comprising a compound having the formula ##STR9## wherein:

• R.sub.1 is hydrogen or lower-alkyl;
• R.sub.2 is hydrogen, lower-alkyl or phenyl;
• R.sub.3 and R.sub.4 are independently hydrogen, alkyl containing 1-8 carbon atoms, benzyl, phenyl, phenyl substituted with 1 or 2 halo, lower-alkyl, lower-alkoxy or di-lower-alkylamino groups, or CR.sub.3 R.sub.4 is cyclopentyl, cyclohexyl or cycloheptyl, provided that R.sub.3 and R.sub.4 are not simultaneously hydrogen;
• and
• Z is naphthyl, biphenylyl, phenyl, phenyl substituted with 1 or 2 lower-alkyl, lower-alkoxy, phenyl, halo or nitro groups or Z is a substituent having the formula ##STR10## where in the above formulas R.sub.5 and R.sub.6 are independently lower-alkyl or benzyl;
• R.sub.7 is hydrogen, lower-alkyl, lower-alkoxy, halo or di-lower-alkylamino, and
• R.sub.8 is hydrogen or lower-alkyl.