Abstract: A dyestuff of the formula: ##STR1## wherein D is the residue of a colored compound of the 6,13-dichlorotriphendioxazine series, the triazine group being attached to a nitrogen atom in D, and wherein:Y is 1 or 2,R.sub.2 is Cl, Br, OH, lower alkoxy, NH.sub.2, a quaternary ammonium group or the residue of a primary or secondary amine,R.sub.1 is H or an alkyl or substituted alkyl group of up to 4 carbon atoms, andR is a hydrocarbon or substituted hydrocarbon radical.The invention provides a range of blue dyestuffs especially useful for reactively dyeing cellulose by heating in the presence of a carbodiimide.