Cast on

Hi there
I have been knitting for many years and am by no means a novice, but I have just come across a pattern that requires me to cast on in a contrast wool, then knit 3 rows, then change to rib by knitting into the loop between each stitch.This is no problem, but then it says remove the contrast wool??? I tried this and lo and behold, it all came undo, which is what I would expect. Cannot understand what this is all about, doers anyone have any ideas??
June

That sounds like a tubular CO or Italian tubular CO, there are some videos for it on Youtube. I think you wouldn’t remove the contrast yarn until you’ve knit several row with the regular yarn, or when you’re done.