The way a hen normally puts an egg together I to add all the bits, then spend hours with the egg in the shell gland, laying on the shell. After the shell is all there, she adds the brown coating in that last half-hour if she lays brown eggs. If you crack that brown egg and remove the membrane from the inside of the shell you can see what that basic shell color is. Or use sandpaper and take the brown coating off. That's an extremely white egg but underneath the two should be the same color.
If something causes the hen to lay the egg early, it can be really light. Maybe she was disturbed while on the nest. If it is a rare occurrence and not a general thing throughout your flock it's no big deal. We are all allowed an occasional oops.
If it becomes widespread throughout your flock, well there are some diseases that can cause that and other weird things with the eggs. But as long as it is only one hen, the other eggs are normal (shape and size as well as color), and it's not an everyday occurrence it's nothing to worry about.
If is just one hen and it happens regularly to her and only her then she is just prone to getting excited when laying eggs. Some are just more high-strung than others.
