Single layers of chalcogenide semiconductors have demonstrated to exhibit tunable properties that can be exploited for new field-effect transistors and photonic devices. Among these semiconductors, Indium selenide (InSe) is attractive for applications due to its direct bandgap in the near infrared, controllable p- and n-type doping and high chemical stability. For its fundamental study and the development of practical applications, rapid and accurate identification methods of atomically thin nanosheets are essential. Here, we employ a transfer matrix approach to numerically calculate the optical contrast between thin InSe flakes and commonly used SiO2/Si substrates, which nicely reproduces experimental values extracted from optical images on 285 nm SiO2/Si substrates. Standard 90 and ∼300 nm SiO2/Si substrates result to provide an optimized optical contrast to detect few layer InSe flakes using monochromatic illumination at ∼450 and ∼520 nm, respectively. On the other hand, calculated optical contrast reveals an optimum value of 110 nm for the thickness of the SiO2 film on Si substrates in order to detect InSe nanoflakes as thin as one single layer, under white light illumination. These results demonstrate that the proposed optical contrast method is a very fast and reliable technique to identify atomically thin InSe nanoflakes deposited onto SiO2/Si substrates.