Comparison between the distribution of the I_E − H_E, u − I_E, and Y_E − H_E colours in the Int and SED mock catalogues. Top row: Euclid Wide catalogues. Bottom row: Euclid Deep catalogues. Significant differences between the Int and SED methods are apparent, most notably with the SED method giving rise to significantly bluer u − I_E colours compared to the Int method. These differences arise when the galaxy templates are unable to closely match the observed broadband SED; this may be due to the photometric redshift being incorrect and/or due to the absence of a template that sufficiently represents the properties of the galaxy.