My wife and I have done a couple of "Painting with a Twist" classes where the usual technique starting out drawing a sky involves putting a base coat down of a dark blue, and then overpainting while wet with different colors to create a blend of streaks. I'm pretty sure I found one of the brushes that did something like this, smearing and blending the colors, but I'm having an issue finding it now. I'm hoping that if I put out a query here, it gives me something to reference in the future.
If using water colors you can re-wet or lift a layer to wet.
Try looking for blender brushes in the style (oil, chalk, watercolor, etc.) you are working in.
Almost any brush can blend well if you know certain settings like re-sat etc. Check the manual to learn those settings, or Google search for blending...using words that fit your situation.
If you have a specific blending question, ask a more specific question and include brush type category.