Thanks for answering, however I, then, have more wonderings.
Ok, then you would say that you could play as well, for instance keeping count with a good harvest. However, keeping count as a 0 cost card need to have a match with an hero ressource icon, and a good harvest does not grant you the icon ressource match as it only stipulates that you could pay with other spheres ressources.
Finally, what is the ruling :
1/ you can play Beorn, but you cannot play keeping count with A Good Harvest
2/ you can play both with a good harvest and no issue with the 0 cost rules (icon ressource match)
3/ You cannot play either card as you need a ressource icon match even for Beorn
My feelings would go to solution 3/ as the card purpose, for me, sounds more orientated to improve 2-3 colors deck playability than providing extra color for a specific card need.