You can now make the random rainbows disappear after leprechaun interaction with a new setting in the config (despawn-on-leprechaun-interact). You can also keep things as normal and let the rainbows stay after leprechaun interaction, until their time has passed, (without the leprechaun).
Notes:
Make sure you regenerate the new config setting if you want to use this version of the plugin.
I have discovered a bug for 1.15 users regarding the leprechaun spawning 1 block underground, resulting in their rainbow not appearing. This will be fixed shortly!