[en] The colouring properties of two coordination compounds previously synthesized by us: 8-(1',2'-naphthyl)- 1-R-3-methyl-6-thiomethyl-4,5,7-triazanona-1,3,5,7-tetraenato-1,1'-diolato( - )-O"1, O"1"', N"4 , N"7 -vanadyl, where R=CH_3 (1), C_6H_5 (2) have been investigated. These compounds meet the requirements to be used as dyes for thermoplastic polymers. Colouring complexes have a high photostability (7 points), thermostability (>250 degrees Celsius) and an intensity of colour, which give a low consumption (0.006 to 0.015 g medium tone, 0.020-0.100 g to 100 g polystyrene intense tone and 0.005 to 0.010 g medium tone and 0.015-0.035 g intense tone for 100 g polyethylene). The investigated compounds stained polystyrene and polyethylene in claret-brick. Compound 2 has a higher thermostability (365 degrees Celsius) than compound 1 (285 degrees Celsius). (authors)