  Colors are usually not used for constraining stellar populations because they
are thought to have the well-known agemetallicity degeneracy, but some recent
works show that colors can also be used. A simple stellar population synthesis
model is widely used, but there is no analysis for its colors. We try to find
colors that can potentially be used to determine the age and metallicity of
stellar populations by the standard model. Principal component analysis and
relative sensitive parameter techniques are used in this work. As a result,
U-K, U-H, U-J, B-K, B-H, U-I, B-J, and V-K are found to be more important for
studying populations than others. Pairs of colors such as B-K and B-V are found
to be able to disentangle the stellar age-metallicity degeneracy via the
high-resolution model, while pairs such as U-K and R-I may be used instead when
the low-resolution model is used. Furthermore, the u-g and r-i colors of the
low-resolution model seem to have the same potential, but there are no such
colors for the high-resolution one. In conclusion, some colors have been shown
to have the potential to determine the age and metallicity of stellar
populations, but relative metallicity and age sensitivities of colors in
different stellar population synthesis models are usually different. In
addition, minor star formations will make star systems look younger and more
metal rich than their dominating populations.
