Observed correlations between the SNIa rate and the parent galaxy U − J (left) and B − K (right) colour in the SUDARE, CET99, and LOSS surveys. For the local surveys the stellar masses of the galaxies have been evaluated with the piece-wise relation discussed in the text. For the LOSS survey we also show as filled symbols the rate normalized to the mass derived from the BJ01-a relation. Colours are shown in the AB magnitude system. The horizontal error bars show the 1σ width of the galaxy distribution within each colour bin; the vertical error bars show the uncertainty on the rate from the statistics of the events.