The variegation on this species seems to be more unstable than it is on the variegated C. speciosus. Sometimes you get totally white foliage on one stem, totally green on another, and all kinds of gradations and patterns in between. I'd remove the plain green stems to encourage the variegated ones, otherwise the green tends to be stronger and may become dominant. Just be sure the ones you leave on have some green in them. The totally white ones can't photosynthesize.

It's somewhat a question in my mind whether one might have to remove the new leader as well as the green canes as the leaders themselves may have "reverted" and just continuously produce green shoots?? If you cut the green ones off and those are subsequently replaced by more solid green ones , you may have to remove that particular leader entirely?? I've been much tempted to try growing the variety in question over the variegated speciosus, because of the much stonger variegation pictured for the "amazonicus", but if "reverting" is such a problem , I may reconsider. I have the "barbatus", but since it's such a reluctant bloomer for me indoors during the winter, I'd thought having one with the much showier variegated leaves would provide more interest and color , even should it never flower. I do like the appearance of the costus in general with their unusual growth habit, but the variegation would be a big plus for me.

Birdinthepalm:
I think removing the stem is sufficient. The plant is ridiculously un-stable, if you want my opinion - I have more of a problem of it producing all white leaves. If I could only choose one, I would go with C. speciosus myself.

You picked a large Costus to grown in a container when you picked C. barbatus, there are a lot of Costus that stay smaller that might be easier in a pot. You aren't cutting the barbatus down before you bring it in for the winter are you? It has to have 2nd year growth to bloom and new growth over the winter inside, doesn't count.

Thank you all for the suggestions and comments! I am now cutting off any all-green stems, so I'll see what that does over time.