blue sleeving

What's with all the blue oil lines?I was lead to believe that YELLOW is Gas , RED is liquid fuel,Gray and blue is electric conduit. I've been installing factory sleeved copper oil lines and they be red and the words fuel oil are printed right on them. Its a problem waiting to happen The other day a plumber cut into a buried 4in. white pvc pipeto make a connection for a sewer line from an addition. The only problem was that when he startred cutting the pipe he got a nice JOLT. Seems somebody used DWV pipe, instead of gray pvc conduit,to run a subfeeder curcuit underground. Hey its buried and its plastic, and it doesn't matter! There is a reason why certain things have a special color coding!