  Let $T(H, G_n)$ be the number of monochromatic copies of a fixed connected
graph $H$ in a uniformly random coloring of the vertices of the graph $G_n$. In
this paper we give a complete characterization of the limiting distribution of
$T(H, G_n)$, when $\{G_n\}_{n \geq 1}$ is a converging sequence of dense
graphs. When the number of colors grows to infinity, depending on whether the
expected value remains bounded, $T(H, G_n)$ either converges to a finite linear
combination of independent Poisson variables or a normal distribution. On the
other hand, when the number of colors is fixed, $T(H, G_n)$ converges to a
(possibly infinite) linear combination of independent centered chi-squared
random variables. This generalizes the classical birthday problem, which
involves understanding the asymptotics of $T(K_s, K_n)$, the number of
monochromatic $s$-cliques in a complete graph $K_n$ ($s$-matching birthdays
among a group of $n$ friends), to general monochromatic subgraphs in a network.
