Representative I vs (V − I) colour magnitude diagram for our synthetic population models. This population has been generated using the Tail metallicity distribution function model and a mean age of 12.5 Gyr. Red circles and blue diamonds represent stars flagged as RR Lyrae using the Marconi et al. (2015) and Smolec & Moskalik (2008) instability strip models, respectively. The dashed black lines mark the intrinsic colour range of our bulge RR Lyrae sample.