Developing semiconductors with wide tunable gain bandwidth have always been at the forefront of laser technologies. The variation in feedback resonators can provide a useful tool for producing a relatively wide range of discrete lasing wavelengths. However, the lasing wavelength range is limited by the fundamental gain bandwidth of the single semiconductor itself. Full-colour range lasing through gain bandwidth tuning remains a daunting challenge. Here we demonstrate the feasibility of dynamically tuning amplification/lasing wavelengths in the entire emission spectrum by leveraging on Förster resonance energy transfer (FRET)-assisted guest-host blends. The unprecedented tunability in amplification and lasing is governed by energy transfer process, which enables us to achieve wavelength-tunable semiconductor lasers spanning the full visible region of the electromagnetic spectrum. Our distributed feedback lasers cover almost all CIE colour gamut (94%), which is 170% more perceptible colours than standard Red Green Blue colour space. These insights can guide the versatile and convenient design of semiconductor materials transcending current gain bandwidth limitation, paving the way for next generation of optoelectronic devices.