The bimodality in observed optical colours is a striking characteristic of the z=0.1 galaxy population. As galaxies are born blue and must transition to the red population, the dearth of galaxies at intermediate colours (i.e. the 'green valley') suggests that this transition must be rapid, at least relative to the age of the universe. It is also follows that galaxies in the green valley may be undergoing, or have recently undergone, a transient quenching phase. But is the green valley a one way street?

While colours are an accessible means to infer quenching and passivity statistics observationally, there are problems. Dust effects and age-metallicity degeneracies render these inferred physical quantities uncertain, and while colours reveal how the ensemble population changes they fail to tell us much about the evolution of individual galaxies. I will discuss how we use forward modelling of the state-of-the-art cosmological, hydrodynamic simulation suite EAGLE to investigate the build up of the galaxy colour bimodality reproduced well by the simulation at z=0.1. I will also discuss how we can identify evolutionary tracks in the colour-mass plane archetypal of different quenching mechanisms in the simulation, and reveal diverse histories; from galaxies transitioning through the green valley rapidly and remaining red to those that pass through several times due to rejuvenation. Additionally, I will present how we can account for dust faithfully using radiative transfer, and the detailed mock observations that are available as a result.