Gamma Velorum is a superb multiple star - all four components visible in a 60mm refractor - though star D at 9.1mg needs good seeing. Colour contrasts are not large, but primary star A, also called Gamma Velorum 2 has a green or pale yellow tint. Its spectral type is O7.5e+WR8. The spectrum has been viewed often and photographed (below). It's possible the blue and yellow emission bands combine with strong violet and green in the continuum to give it a green or violet tint (?) Secondary B (type B) is very blue to my eyes, and C and D seem white (both type A)
Gamma Vel is the brightest of the rare type O stars - none are close to Earth (thank heavens!) and the second brightest is nearby Zeta Puppis. Both are sited within the Gum Nebula, a recent (~5000y BP) and huge supernova remnant. The whole region is rich in stellar exotica.
(This is a sketch - photos of this object are usually much overexposed)