  Colour-M/L (mass-to-light) relations are a popular recipe to derive stellar
mass in external galaxies. Stellar mass estimates often rely on near infrared
(NIR) photometry, considered an optimal tracer since it is little affected by
dust and by the "frosting" effect of recent star formation episodes. However,
recent literature has highlighted that theoretical estimates of the NIR M/L
ratio strongly depend on the modelling of the Asymptotic Giant Branch (AGB)
phase. We use the latest Padova isochrones, with detailed modelling of the
Thermally Pulsing AGB phase, to update theoretical colour-M/L relations in the
optical and NIR and discuss the consequences for the estimated stellar masses
in external galaxies. We also discuss the effect of attenuation by interstellar
dust on colour-M/L relations in the statistical case of large galaxy samples.
