I have only been embroidering since Sept. and every time I do I substitue colors/brands. I have one rule when I buy thread and this is after embroidering a few things and this seams to be the trend. Say if I buy a certain shade of blue, I buy another one that can be used to shade or highlight it. Most designs that I've used have needed two shades for the sky or two shades for the trees, etc. So I try to get at least one or two a shade or two different from the main one I'm buying. I use mostly rayon but have a few embroidery polyester and have substituted them in. And yes, just recently I had to use a regular polyester because none of the embroidery shades I had could substitute for what I needed and it was too late to run to the store. It was a small section and not too noiticable in the end anyways. I'm continuing to collect my threads. We have a LQS here that has had their RA on sale BOGO for over a month and every payday I go there (over 30) miles and pick up a bunch. Last time I got $90 worth of thread for 45 so that was worth the time and gas to go there. There are toooooo many different companies and shades to even try to get them all. When ever possible I use the thread conversion chart to show me the thread colors in the main brands that I buy and that helps me get a little closer to what I need.