Birds are some of the most colourful organisms on Earth - no wonder they are one of the most studied models in the evolutionary ecology of colour signalling. However, even though we devised very precise ways to measure their colouration - we are far from understanding the genetic and phylogenetic factors that shape their colourful signals. One of the most important factors contributing to the large heterogeneity of results related to avian plumage colouration is the simplifying nature of measuring just one level of the underlying complexity of colour producing traits. In my talk I will discuss the way variation in bird colouration can be seen when partitioning it into its multiple causal components. I will use two model systems - the blue tit and the house sparrow - to show how changing the perspective may shift the resulting conclusions. On a higher, more comparative level I will show how focusing more on mechanisms may yield new inferences about the evolutionary dynamics of bird colouration.