Which postoperative treatments do you recommend for people with colon cancer?

Depends on Stage: The stage of colon cancer is dependent on the depth of the cancer in the colon wall as well as the presence of cancer in adjacent lymph nodes, organs, or distant sites. Depending on the stage, chemotherapy +/- radiation therapy may be indicated.

Stage dependent: Postoperative therapy is stage dependent. For stage 1 cancer usually just follow-up is enough; for high-risk stage 2 cases chemotherapy or clinical trials are considered; for all stage 3 and 4 cases chemotherapy is recommended; radiation is usually not required unless tumor was attached to other structures or couldn't be entirely removed for example.