Here is a page from my watercolor journal painted on Sanibel Island, FL. There are two distinct brush techniques. The top image, a Ruddy Turnstone, was made by applying paint. It became darker and darker. The brush is continually loaded with paint. The lower image, Sanderlings, has a different technique. First the paint is applied and then it is removed. I used a clean brush with water and scrubbed the paint off. It leaves beautiful "edges".
Some painters believe a great painting is all about edges!