Is it possible to simulate the behavior and interaction of two fluid systems with different particle properties and colours?
Yes, but it would be largely on your side to implement the interaction.
GVDB Voxels is a developer library which provides the basic tools. Neighbor searches, voxel computation, and raytracing. Specifics of the simulation are up to the developer, and two fluids would be in this category. Using the gFluidSurface sample you could, for example, add additional properties to each fluid particle and use those during force calculations. Particle color is already a property in that example which can be rendered.