Colour and magnitude variations for two different time intervals. The top-left panel shows the variations in R − I,I, and R. The other three panels show colours and magnitudes for wavelengths up to 4.5 μm. No colour variations are evident for the R − I and J − K colours, while strong variations are visible for λ ≳ 2   μm. In these later cases the star becomes redder when becoming fainter (see also Fig. 9).