Colour−colour diagrams for the cluster region in N159W (left-hand panel) and the control region (right), with the loci of the main sequence (MS), giant branch, and T Tauri stars (TTS) overlaid in red, orange and blue, respectively. Also shown are reddening vectors (dashed red lines) drawn from the tip of the giant brach (left), from the base of the MS (middle), and from the reddest TTS (right). Cluster sources with a NIR excess are indicated in the left-hand panel by the blue circles. The error bars in the lower-right corner show the average uncertainties in the colour terms.