The white light laser I worked with ( bear in mind this is back in 1990) were mixed gas argon and others cant remember now, they were in reality a very pale green colour but when put through a dichoric filter you could get the colour spectrum, The reds and yellows were poor in comparison to the green and blues, The laser itself was built specially for entertainment use by a company called coherent who also made scientific lasers, we also used lasers by a company called spectra physics.
To get a 4 watt output from the laser you needed a 3 phase 32 amp supply and about 3 gallons a minute cold water flow for the cooling system. The laser tube was in a glass water jacket bit scary when you think aboput the 30000 volts needed to get the plasma to lase.
I think the hire and entertaimnet industry has moved on a bit since I was involved and you can now get a lot of light output for not much energy input, yag lasers are used now I think
Howard