NUV – r colour plotted against the absolute magnitude in the r-band. The red region denotes the space occupied by the red-quiescent galaxy population, while the blue region represents the blue galaxy population (Singh et al. 2019). Magenta dots represent LSBGs, and red crosses represent UDGs with NUV detection in our sample. Green stars indicate the upper limits of NUV – r for UDGs in Abell 194 without NUV detection. Upward cyan triangles and black plus symbols represent UDGs from the Coma cluster reported by Singh et al. (2019) and Lee et al. (2020), respectively. Downward navy blue triangles and pink rhombuses denote the upper limits of NUV – r for UDGs in the Coma cluster from Singh et al. (2019) and Lee et al. (2020), respectively.