We have produced silver colloids by ablating metal targets in water and using two different laser wavelengths. The obtained sols have been characterized by optical spectroscopy and electron microscopy, revealing a definite double size distribution centered at a few tens and a few hundreds of nanometers with a mild difference between the two wavelengths employed. On the contrary, a marked difference in shape has been found for the biggest aggregates, revealing sharp cubic or octahedral structures when visible or infrared radiations are used, respectively. This fact is explained by the re-irradiation processes induced on the already formed colloid and taking place during the ablation.