Blurring and smudging are not possible in Concepts. Concepts draws with vectors instead of pixels, and doing blur and smudge in real-time is not feasible on current mobile hardware. In raster apps, it's easy to rearrange a flat set of pixels; in Concepts, every time you zoom or pan, everything gets redrawn. This is what allows for those crisp, un-pixelated strokes when you zoom in.
If you'd like to mimic the effect of a blur, you can use the Soft Mask at varying opacities to gently lessen the opacity of your strokes and thus "blend" the colors together. You can use it to soften or blend stroke edges, or create gradients of colors drawn on top each other. This tool works same-layer only. Use it at a large size for greater diffusion.
Another method is to use the Airbrush, which is a soft-edged brush, and blend colors by lowering the opacities of the strokes. You can create some realistic gradients this way.
Concepts' vector watercolor brush (not the same tool as the Matthew Baldwin watercolor brushes) live-blends same layer with other watercolor strokes, giving a "wet brush" bleed appearance.