A three-channel spectrometer is constructed with a 460 nm high brightness light-emitting diode (LED) source (250 mW peak optical power output, 1 mm sq, 150 μm thick) and a red-green-blue (RGB) image sensor (3 × 4 mm, 1 mm thick) for purposes of a small form factor spectrometer to monitor reflectance/emission spectra from chemical wet etching experiments. The linearity and spectral response of the RGB image sensor is characterized and a three-channel spectral model is fitted to the extracted spectral response. We use this information to quantify time developments of the RGB image sensor outputs for in situ copper and aluminum etching experiments in terms of three defined spectral bands.