I made a Global.gd to remember how it was made and declared color_change()
in Torch.gd file.
PlayerDetection.gd:
func _process(delta):
torch.change_color(player_is_in_FOV())
Torch.gd:
func change_color(player_in_fov):
if player_in_fov:
light2d.color = RED
else:
light2d.color = WHITE