Recently, colorless and transparent plastic substrates with high glass transition temperature and suitable thermo-mechanical properties are in high demand in optoelectronic device industries, due to their various optical applications. Colorless polyimides (CPIs) exhibit both high thermo-mechanical stability as well as high transparency that are suitable for optoelectronic applications. The most recent (2010–2018) developments on CPIs, in terms of design and synthesis of new monomers and their effects on the thermo-optical properties of the obtained CPIs, are reviewed in this article. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim