Other than a text label that defines the content and/or manufacturer, the only thing I have ever seen in the way of color coding is the 4 color diamond on the side with a number in each of the colors.
The colors are always the same (Red on top, Blue on the left, Yellow on the right and White on the bottom), so the colors are meaningless except to try to differentiate (just in case the symbol is not "upright") which attribute of the contents the number is specifying something about. The attributes are something like volatility, flammability, taste and fashion sense, ... no wait, it is "Fire Hazard" [Red], "Health Hazard" [Blue] "Reactivity" [Yellow] and "Specific Hazard" [White]. (Might as well be Flammability, Poisonability, Eat your flesh off-ability and Fashion sense-ability.)
The numbers represent something about each of those attributes of what is in the drum (or box or building or anything else that the symbol is on), but what the numbers mean in each color is just like trying to remember what the colors mean... they are only known to those that have to deal with it every day. To the rest of the populace they are just pretty colors and sometimes mean that the container probably has something scary in it.
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