Color–color diagram for the 2008, 2009 and 2011 seasons (black bold dots) of the two lensed components “A” and “B” of UM673. The “B+G” values are relative to the color indices of the “B” component that includes the contribution of the lens galaxy, as in the approach of Koptelova et al. (2010b). The diagram also includes HST (Muñoz et al. 1998) data (black light points) and Koptelova et al. (2010b) data (little gray points). The larger background symbols refer to the data from Koptelova et al. (2012).