Generally the green stuff is "conventional", the orange stuff is "extended life". They use different additive systems which in some cases may be incompatible and precipitate deposits. Not really a big problem, but some people who are concerned will pass on the warning with emphasis. Then there's the ongoing preferences between propylene glycol, and ethylene glycol........so here's a link to the Peak site with some discussion on these and other matters of antifreeze. From the page linked, go to the bottom for the other subject matters discussed.

http://www.peakantifreeze.com/tech/tech_e.html