  We investigate the two-dimensional four-color Ashkin-Teller model by means of
large-scale Monte-Carlo simulations. We demonstrate that the first-order phase
transition of the clean system is destroyed by random disorder introduced via
site dilution. The critical behavior of the emerging continuous transition
belongs to the clean two-dimensional Ising universality class, apart from
logarithmic corrections. These results confirm perturbative
renormalization-group predictions; they also agree with recent findings for the
three-color case, indicating that the critical behavior is universal.
