Comparison of observed S₂₅₀/S₂₄ colours for sources with flux densities between 3 <S₂₅₀< 5.7 mJy selected by their associated photometry accuracy from the simulations. The median colours of sources with a good photometric accuracy | ΔS | /S_out≤ 0.32 (black line) follow the colour trend, of clean-selected sources CI ≤ 1 (blue line) and the stacked sources (orange line) while the median colours of sources having poor photometric accuracy | ΔS | /S_out> 0.32 (red line) are systematically displaced to brighter 250 μm fluxes, an indication of blending.