The invention relates to a method for producing liquid, storage-stable isocyanate mixtures comprising carbodiimide (CD) and/or uretonimine (UI) groups, with low colour index. The invention also relates to the isocyanate mixtures obtained according to said method and to the use thereof for producing mixtures comprising additional isocyanates and/or for producing prepolymers with isocyanate groups and polyurethane plastics, preferably, polyurethane foams.