The VL4 wasn't actually the first washlight in Vari-Lite's new Series 200 family - that was the tungsten-lamped VL3. The VL4 followed a few years later, using the same 400W HTI arc lamp as the VL2B for greater light output. 
Unlike the VL2, it was a CMY colour-mixing fixture using a system Vari-Lite called Dichro*Tune. It had a variable diffusion system to allow its beam to go from a 4 degree spot to 28 degree flood. The combination of colour and diffusion could produce some quite ethereal effects. 
Usually used alongside its companion VL2 spotlight, and later supplemented by the tungsten VL5 washlight, the VL4 also became a mainstay of concert touring and theatre. Towards the end of its life, both it and the VL2 even gained the ability to be controlled by DMX from consoles other than the Artisan. Track down Pulse, the video of PInk Floyd's 1994 Division Bell concerts, to see this Vari-Lite family really put through their paces. 

VL4
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VL4
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