This is based on coding challenge 59 from the http://codingtra.in/. It uses the Edge of the Galaxy font.
The iframe src attribute can include query fields c and m as follows:
<iframe style="width: 620px; height: 420px;" src="https://psb-david-petty.github.io/p5js/coding-train-cc-59/src/?c=000080&m=This+is+a+test"></iframe>
In this case, the linked sketch displays the text This is a test on a Navy blue background (#000080).
Note: According to this answer, p5.js now makes it impossible for embedded sketches (linked with https://editor.p5js.org/) to parse URI parameters. Therefore, the entire sketch is hosted in the src directory of this repository so the URI parameters can be parsed.