Comparison of our observation (left panels) with synthetic population models (right panels). The difference in the (u − g)₀ and (u − i)₀ colors, with similar (J − K_s)₀ color, between the bRC and fRC can be reproduced with two-population models. The bRC models (red circles) are enhanced not only in [Fe/H] but also in He abundance with respect to the fRC models (blue circles) with Δ[Fe/H] = 0.5 dex and ΔY = 0.1.