The main page, including source code, is on GitHub. All of the javadocs for the latest (built) version of code are in subdirectories of this site. You can also download javadocs in a .jar for released versions of SquidLib using Maven, Gradle, or simply by going to the Maven Central page for SquidLib and downloading the jars you want. As for javadocs...
Because visualizing what an SColor (from the text rendering part) looks like in contrast to others like it can be a challenge, there are some quickly-made large tables of every SColor defined by the library. You can view the colors sorted alphabetically by name, sorted by hue, or sorted from darkest to lightest.