Property $\star$ for $G(n, 1/2)$ holds with high probability: for every $\varepsilon > 0$ and all large $n$, the probability that $G(n,1/2)$ contains a subset $S$ of size $\geq n / (\log_2 n)^2$ none of whose $(k_0 - 3)$-subsets is independent is at most $\exp(-n^{1-\varepsilon})$.
Bollobás's theorem (Theorem 8.3.2, Bollobás 1988). With high probability, $\chi(G(n, 1/2)) \sim n / (2 \log_2 n)$. Concretely, for every $\varepsilon > 0$ and all large $n$, $G(n, 1/2)$ is colorable with $n/(k_0 - 3) + n/(\log_2 n)^2$ colors with probability at least $1 - \exp(-n^{1-\varepsilon})$.