Water soluble solid colours and basecoats are now commonly used by paintshops, largely because of stricter regulations regarding VOC (solvent) content in traditional car paints.
Water based car paints are now relatively common in professional bodyshops, having been used several years earlier by most manufacturers. Available as solid colours and metallics, they perform the same purpose as conventional basecoats, producing an even coloured matt substrate which is then protected by a clear lacquer. Thinners used in these products has very little solvent and tends to be alcohol based rather than petroleum. The main difference in their use by anyone more familiar with traditional car paints is the working conditions best suited to their use.
Application is not really that much different to any other paint (as always follow the manufacturers instructions), but drying is a different matter. Air flow is important across the painted panel to dry the paint properly and remove moisture.
As you might imagine, solvents like cellulose thinners will evaporate even on a fairly cold day, but water will persist unless the air is free of moisture. Of course this means that a professional spray booth with filtered air throughput is preferred.
This doesn't mean that water based materials can't be used without a spray booth, just that extra care needs to be taken to make sure the material is thoroughly dry before any lacquer is applied, otherwise serious problems can arise with microblisters and lack of adhesion.