Graph Coloring · Easy problem

Six tasks $T_0,\ldots,T_5$ must be scheduled into time blocks. The conflicting pairs (which cannot share a block) are $T_0\&T_1$, $T_0\&T_2$, $T_1\&T_2$, $T_0\&T_3$, $T_3\&T_4$, and $T_4\&T_5$. Using the greedy-coloring bound $\Delta(G)+1$ — without running the algorithm — what is the most blocks this bound could ever force, no matter what order the tasks are colored in?