Most likely, the extra stuff that is added to colored, store brand lye is sodium nitrate, and aluminum pellets, and of course, color. Sodium nitrate is a well known carcinogen, and, the store stuff usually contains very high quantities of it. If you find the MSDS for the product you're looking at, you'd probably find that it contains only about half sodium hydroxide, with 40% sodium nitrate, and the rest aluminum and other impurities.