I have also had plain green leaves on a variegated cast iron plant. When repotting, I found that some of the branches/offshoots on the rhizome were growing completely green leaves. I cut these branches off of the rhizome. It was like when an upright variegated plant grows a reverted branch with 100% green leaves. Have you noticed this happening on your cast iron plant? I also really like plants with variegated leaves. My favourite that I have found so far is variegated abutilon (Chinese lantern); Mine is almost completely white but still quite vigorous.

I have just the green leaf one outside in my garden under a palm tree and I absolutely love it!!

lovelove forevers sweeties @w