  We conjecture an exact form for an universal ratio of four-point cluster
connectivities in the critical two-dimensional $Q$-color Potts model. We also
provide analogous results for the limit $Q\rightarrow 1$ that corresponds to
percolation where the observable has a logarithmic singularity. Our conjectures
are tested against Monte Carlo simulations showing excellent agreement for
$Q=1,2,3$.
