Two-color excitation of a hydrogen atom has been studied by solving the time-dependent Schrödinger equation. We have chosen the two laser frequencies to be the fundamental and its third harmonic with an adjustable phase between the two laser fields. This has been proposed and successfully implemented in the past for "coherent control" of atomic and chemical processes. Here we have extended the study to the high-intensity domain and well into the tunneling and the stabilization regimes. We show that in the tunneling regime the two-color excitation can enhance the intensity of harmonics by more than two orders of magnitude compared to a single color at the same effective intensity. In the stabilization regime we confirm that two-color excitation can be used to generate higher harmonics.