Has the bulb grown to a size to flower? If not it is simply dying back and will grow again next year.

Cardiocrinum should really be in full growth right now - all mine are and still have a way to go. There are many reasons why yours might be turning yellow. It could have dried out or conversely got too wet, it might be reacting to the wrong substances in the soil, it could have been damaged by weedkiller spray drift. Would need to know how & where you are growing yours.

I am growing the lily in a large planter,have it indoors.