Grey Colouring Photochromic Fused Pyrans

A photochromic grey colouring 2$i(H)-naphtho[1,2-$i(b)]pyran of formula (I) wherein R?1¿ is selected from mono-, di- or poly-substituted aryl groups, mono-, di- or poly-substituted naphthyl groups and mono-, di- or poly-substituted heteroaryl groups, wherein at least one substituent is a nitrogen containing group, including amino, C¿1?-C¿20? and C¿6?-C¿20? alkylamino, C¿1?-C¿20? and C¿6?-C¿20? dialkylamino, C¿2?-C¿20? dialkenylamino, C¿2?-C¿20? or C¿4?-C¿20? di(polyalkenyl)amino, arylamino, diarylamino, C¿1?-C¿20? alkylarylamino, tetra (C¿1?-C¿10? linear or branched alkyl) guanidino and cyclic-amino groups and at least one of R?7¿ and R?9¿, which may be the same or different, is selected from C¿1?-C¿20? $i(N) alkylamino C¿1?-C¿20? $i(N)-alkylamido, C¿1?-C¿20? $i(N,N)-dialkylamido, amido, nitro, amino, C¿1?-C¿20? alkylamino, C¿1?-C¿20? dialkylamino, C¿2?-C¿20? dialkenylamino, C¿4?-C¿20? di(polyalkenyl)amino, arylamino, diarylamino, C¿1?-C¿20? alkylarylamino, or cyclicamino groups. The compounds may be combined with a polymeric host material such as plastic or glass to make a sunglass lens, an ophthalmic lens or a window. The compounds may also be included in an ink or a fuel.