RATIONALE: Vorinostat may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Drugs used in chemotherapy, such as fluorouracil and leucovorin calcium, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. It is not yet known which dose of vorinostat is more effective when given together with combination chemotherapy in treating patients with metastatic colorectal cancer. PURPOSE: This randomized phase II trial is studying the best dose of vorinostat to see how well it works when given together with fluorouracil and leucovorin calcium in treating patients with metastatic colorectal cancer that has not responded to previous treatment.