Color gradient vs. apparent luminosity (upper panels) and color gradient distribution (lower panels) for morphological subclasses 1–5, defined in Table 5. In each panel, we highlight one subclass and show the respective other sources as gray symbols. The color gradient is measured as the difference between the aperture 2 (A2) color with r = 2 r₅₀ and the aperture 1 (A1) color with r = 1 r₅₀. The figure only includes sources with r₅₀ ≥ 4 pixels.