Display omitted •Terpyridine based sensor for multi ions with different colors.•Terpyridine incorporated hydrogel for practical utility in aqueous medium.•RGB-Arduino multiple chemosensor detecting system was successfully developed. A multi cation sensor based on a terpyridine moiety was successfully designed and synthesized. The sensing behavior of the developed probe was monitored via colorimetric and fluorimetric methods using UV–vis and a fluorescence spectral technique. Each metal ion (Fe3+, Co2+, Hg2+, and Sn2+) exhibited a different color, indicating the high selectivity of the developed probe. A hydrogel sensor, prepared for practical utility, displayed the same colors for each ion as the visual detection experiment. Furthermore, an RGB-Arduino multiple chemosensor detecting system was developed to measure the presence of ions such as Fe3+, Co2+, Hg2+, and Sn2+.