A colorimetric chemosensor based on a novel Schiff base 4-chloro-2-[(3-(4-(dimethylamino)phenyl)allylidene)amino]phenol (L1) was designed and synthesized. Experimental results indicated that L1 in solution of DMSO has selectivity toward Ni2+ dissolved in water, showing binding-induced color changes from faded yellow to deep orange, and with stable colorimetric response even in the presence of other ion metals. The presence of Hg2+ promotes a moderate and non-stable color change, producing no interference with Ni2+ detection. An important advantage of L1 as chemosensor over other reported sensors is the simplicity of its chemical synthesis and the possibility to detect nickel ions in water. Furthermore, this novel colorimetric chemosensor exhibited a spectroscopic detection limit of 1 × 10−7 M and by naked eye this recognition limit is 5.4 × 10−6 M.