This sulfonated leuco dye precursor is then oxidized in the same manner asdescribed in step (f) above.The starting materials for use in step (a) may be prepared, for example,(1) by reacting sulfonefluorescein dichloride with a substituted aniline, ##STR17## wherein R.sup.2 is an electron-withdrawing group having a positive sigma value greater than 0.6 to give the mono-substituted sulfonefluorescei