A sensory wall provides an alternative for little hands and bodies to explore and learn. Toys do not always belong on the toy shelf or in a toy bin. In addition, the young explorers are in a vertical position, which is great for establishing additional gross and fine motor control.
If you are working with a child who is uninterested in writing or coloring, my advice is this: Stop worrying about coloring and start by engaging them in what they are interested in! Over time you can begin to shape their interest into a writing activity as well as build the fine motor skills they need for writing.