Breast muscles (pectoralis superficialis, n = 36) constituted the material investigated. They were derived from Big 6 turkey toms. The birds were slaughtered under the industrial conditions. The colour brightness (L*) was measured on the right wing breast muscle from inside (from bone) 24 h post mortem. The muscles were divided into three groups according to their co-ordinate of brightness: L* < 40 (I), L* 40 ≤ L*< 46 (II) and L* ≥ 46 (III). The quality differentiation of the muscles investigated was determined with regard to the selected distinguishing factors of the functional properties of proteins. The lowest solubility values of the total proteins (20.29 g / 100g) and sarcoplasmatic proteins (7.85g/100g) were stated in the group of muscles with a three chromatic co-ordinate reaching a L* ³ 46 level if compared with other groups of muscles. The darkest muscles (L*₂₄ < 40) were characterized by the deepest coefficient of emulsion instability (suitably for I, II and III group: Wn = 33.21 cm³/100g, 38.72 cm³/100 g, 42.28 cm³/100 g). The gelatinising capabilities of homogenates were higher in the group of muscles with L* < 40 if compared to the muscles from the two other ranges of brightness.