The use of pigments and colours is well spread in the history of human beings. There are traditional colour applications such as textile and painting, and new industries, such as make up, agriculture, and food industry. Many traditional pigments are toxic, that's why the attraction to natural pigments grows day by day. The most common natural pigments include anthocyanins. In this talk I will report on a theoretical study, based on time-dependent density-functional theory, of various factors affecting the optical properties of a few representative anthocyanins (mainly cyanin). I will introduce the multi-scale method that combines classical and ab inition MD with TDDFT for computing the absorption spectra of a given molecule. In the end, I will focus on how the geometry changes of the dye affect the absorption spectra of the molecule.