The cofilamentation of two ultrashort laser pulses at 800 and 400nm in argon is numerically shown to counteract their temporal splitting. The output pulses are as short as 15 and 6.5fs, respectively, without any postprocess compression or stringent alignment. The simultaneous generation of two sub-millijoule (160 and 15μJ, respectively) sub-six-cycle pulses at ω and 2ω is of particular interest for attosecond science.