Discussed is a composition of an organic insulating layer comprising a photosensitizer, a binder, an additive and a solvent, wherein the photosensitizer includes a photoacid generator (PAG), and a thin film transistor substrate and display device using the same, wherein the composition of the present invention enables to realize a simplified process by omitting an additional entire-surface exposing process for a color change, and a baking process after an exposing process; and to minimize a problem of color-coordinates shift by realizing a good light transmittance.