Jones and Rosso gave a formula for the colored Jones polynomial of a torus
knot, colored by an irreducible representation of a simple Lie algebra. The
Jones-Rosso formula involves a plethysm function, unknown in general. Our main
result is an explicit formula for the second plethysm of an arbitrary
representation of $\fsl_3$, which allows us to give an explicit formula for the
colored Jones polynomial of the trefoil (and more generally, for $T(2,b)$ torus
knots). Our formula is different from the one given by R.