This leaf is getting a distinctly yellow undertone. I'm worried about the plant. Otherwise it seems healthy.
First let me say I think that is a Alocasia not Colocasia. If this is the oldest leaf that is turning yellow you shouldn't have anything to worry about. As the plant grows it pulls the nutrients back out of the old leaves.
Yes someone else pointed out that it is an Alocasia. I hope it is just an old leaf dying. I love that plant, it's such a willing and strong grower.