This seminar discusses a new graph colouring model aimed at optimizing energy-efficient resource reservation in heterogeneous IaaS cloud data centers. It introduces an integer linear programming (ILP) formulation and an energy-efficient graph pre-colouring (EEGP) heuristic to improve scalability and reduce convergence times compared to the exact algorithm. Performance evaluations demonstrate EEGP's effectiveness in minimizing energy consumption while managing virtual machine requests and server resources.