The Picard Reading List currently includes the novels and comics which have included references to elements of the wider Lit-verse, or to each other. Since this 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.
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.