Early-type dwarf galaxies are not simply featureless, old objects, but were found to be much more diverse, hosting substructures and a variety of stellar population properties. To explore the stellar content of faint early-type galaxies, and to investigate in particular those with recent central star formation, we study colours and colour gradients within one effective radius in optical and near-infrared bands for 120 Virgo cluster early-type galaxies. Twelve galaxies turn out to have blue cores and we find them to have the strongest age gradients, i.e., the youngest central regions. Moreover, the metallicity gradients of almost all early-type dwarf galaxies are found to be negative, indicating metal-enriched central regions. A cluster environment is expected to influence such low-mass galaxies through tidal forces through interactions with other galaxies (harassment) as well as through the ram-pressure of its hot intracluster medium (ram-pressure stripping). Therefore, we are comparing the observed stellar population gradients with model predictions, in order to investigate how ram-pressure stripping and harassment can affect a galaxy's star formation activity and stellar population distribution depending on the galaxy's orbit and the time it entered the cluster.