Blue- and green-emitting laser heterostructures, incorporating InGaN/GaN quantum dots as the active medium have been grown by molecular beam epitaxy. The quantum dot growth parameters have been optimized to obtain the highest photoluminescence intensity and radiative efficiency in the blue (λ=420 nm) and green (λ=545 nm). The blue and green lasers are characterized by threshold current densities of 930 A/cm2 and 1.65 kA/cm2, respectively, under quasi-continuous wave bias. To further reduce the threshold current density in the green-emitting devices, a tunnel injection scheme is used to inject cold holes into the quantum dot lasing states. These devices are characterized by a reduced threshold current density of 945 A/cm2. The measured differential gain in the blue-emitting lasers is 2 x 10-16 cm2. Slope efficiencies of 0.41 W/A and 0.25 W/A have been measured, corresponding to differential quantum efficiencies of 13.9% and 11.3%, in the blue and green lasers, respectively.