I think it just has less brown on the outside, like how a brown egg chicken can lay lighter brown or almost white eggs sometimes.
That occasionally happens when a hen is not getting enough calcium. If the shells of those eggs are thinner than normal, check how much calcium is in their food and whether they have oyster shell available.
But if the shells are the usual thickness, it's nothing to worry about. Less brown on the eggs is a common thing when a hen has been laying for a while. It's most obvious in hens that lay really dark brown eggs, but can happen to any hen who lays eggs with brown on the outside. (Green eggs are blue eggs with brown on the outside. Blue eggs don't have the brown coating.)