Yes, you can, so long as they are the artist's watercolor. The general rule of thumb is that acrylic paint is used for models and primer coats of color because it gives a smooth finish to the plastic model. But when watercolors are used on top of regular acrylic, it creates a light effect that really makes the colors pop. This is great when you want to use different colors in your project but don't want them to clash too much or to cover up certain areas altogether. For best results, mix several colors to create your desired hue before spraying it onto your model in its final design location. And considering how porous, regular vinyl polymers are against color absorption or variations in shade due throughout time, you can't go wrong with watercolors when your final design calls for layering various colors!