Full points represent the position on the HR diagram of grey (squares) and non-grey (triangles) stellar models with mass in the 0.070.6 M_⊙ range, at the age of 12 Gyr. The colour highlights the same mass of the two sequences. For grey stellar models of mass 0.07 M_⊙ and 0.08 M_⊙, and for the non-grey 0.07 M_⊙ model, the evolution in the age range from 8 to 12 Gyr is displayed, the points indicating the position at 12 Gyr.