  The determination of stellar populations of galaxies are important for
studying the formation and evolution of galaxies, because all galaxies contain
many stars and they evolve with galaxies. Spectra data are usually used to
determine the stellar populations of nearby galaxies as they have the ability
to disentangle the degeneracy between stellar age and metallicity. However, it
is difficult to give similar studies to distant (e.g., $z >$ 0.3) galaxies
because of the lack of reliable spectra data. This is actually limited by
current observational equipments and methods. In fact, the information of the
stellar ages and metallicities of distant galaxies are crucial for solving the
problem of galaxy formation and evolution. Colours can give us some information
of the stellar populations of distant galaxies. In the paper, I introduce our
works about using colours to estimate the ages and metallicities of the stellar
populations of galaxies. Some potential colours for studying stellar-population
parameters (age and metallicity) and their sensitivities to stellar-population
parameters are reviewed. A new composite stellar population model that includes
both single stars and binary stars is also introduced.
