The present invention relates to a modified colorant comprising a colorant having at least one polymer attached or adsorbed thereto. The polymer comprises at least one functional group, and various embodiments of the functional group are disclosed. For each of these embodiments, preferably the functional group has a defined calcium index value. Also disclosed are various uses for these modified colorants, including inkjet ink compositions. Thus, the present invention further relates to an inkjet ink composition comprising a) a liquid vehicle, b) at least one colorant, and c) at least one polymer comprising at least one functional group as described herein.