I have no idea what "Horizon" is, but you could cobble something together using Excell.
You want to print a strip that has sections that align with each Function key. (The strip can be taped directly above the keys).
In WordPerfect the keys had a normal state, a Ctl-Fx state and an Alt-Fx state. Your application may have something similar. So each key block may need to contain three entries. You can use normal, bold and bold italics to indicate each key state, or color.