The Discovery Reading List currently includes the novels and comics which have included references to elements of the wider Lit-verse, or to each other. In addition, references in parts of Star Trek #400 and Star Trek #500 connect Discovery stories from those works.
Since the Discovery Reading List does not have a main storyline, as many of the other series do, the light blue denotes the expanded storyline of the television series. Read any or all of these to go a bit deeper. The grey denotes every other connected story, regardless of overall continuity.
As always, not every reference to every other story is mentioned, just the one I chose as most important to show the expanding Lit-verse web.