The colour of denim fabric, which has a large share in the textile market, is an important parameter together with comfort properties during usage. While some users prefer the colour of denim fabrics to have different colours as they use them, others want to be provided with colour stability of the fabrics during use. In this study, the effect of a sol‐gel technique on indigo dyed denim fabrics was investigated. The aim was to reduce the colour change that occurs in denim fabrics as a result of external factors by using silica‐based coatings. The sols were prepared by using TEOS (tetraethylortosilicate) and different volumes of GPTS ((3‐glycidyloxypropyl)trimethoxysilane) as precursors in acidic and alkaline conditions. Synthetic indigo dyed cotton denim fabrics were treated with the sols by applying the pad‐dry‐cure method. It was determined that the colour strength of the treated samples increased and the fabrics treated with the sols prepared in alkaline condition became darker compared to the sols in acidic condition. It is seen that the use of crosslinkers while preparing the sol could improve the rubbing and washing fastness of commercial denim samples.