This invention concerns an injection moulding process for soles having a coloured treading surface produced with expansible and cross-linking "EVA" compounds involving the use of coloured inserts (5) moulded with the same moulding material used for sole, but of a different colour, fed into cups (4) on the bottom of the mould impression and shut by caps (8) also moulded in the same material used to mould the soles.