A process for the preparation of a solid catalyst component made from or containing a Ti compound, a coloring agent and optionally an electron donor on a Mg chloride based support, including step (a), carried out at a temperature ranging from 0 to 150° C., wherein (i) a Mg-based compound of formula (MgClmX2-m).nLB, wherein m ranges from 0 to 2, n ranges from 0 to 6, X is, independently halogen, R1, OR1, —OCOR1 or O—C(O)—OR1 group, wherein R1 is a C1-C20 hydrocarbon group and LB is a Lewis base, is reacted with (ii) a liquid medium made from or containing a Ti compound having at least a Ti—Cl bond in an amount such that the Ti/Mg molar ratio is greater than 3; and an organic coloring agent is present either associated to the Mg-based compound or dispersed in the liquid medium made from or containing the titanium compound.