  From a multiple scale analysis, we find an analytic solution of spherical and
cylindrical Poisson-Boltzmann theory for both a 1:2 (monovalent co-ions,
divalent counter-ions) and a 2:1 (reversed situation) electrolyte. Our approach
consists in an expansion in powers of rescaled curvature $1/(\kappa a)$, where
$a$ is the colloidal radius and $1/\kappa$ the Debye length of the electrolytic
solution. A systematic comparison with the full numerical solution of the
problem shows that for cylinders and spheres, our results are accurate as soon
as $\kappa a>1$. We also report an unusual overshooting effect where the
colloidal effective charge is larger than the bare one.
