High-order harmonics were generated in a two-color scheme exploiting an infrared parametric source with self-stabilization of the carrier-envelope phase. A significant cutoff extension was observed with respect to single color, 800 nm driving pulses at comparable peak intensities. Exploiting the wavelength tuning of the parametric source in the 1.5–1.6 micron range, a continuous xuv spectrum extending from 36 to 70 eV was generated in krypton. A broader xuv continuum, extending beyond 100 eV, was observed in argon. These results represent a step forward in the extension of attosecond science toward the soft x-rays region and open new perspectives in the investigation of quantum effects in atoms and molecules.