Louisiana has two herons that are medium in size (comparable to Snowy Egret), elegant in shape, and mainly or entirely blue. They are easily told apart by belly coloration: white in Tricolored, blue in Little Blue.
The Little Blue Heron has a maroon neck and blue body. The Tricolored is more complex in coloration above, with details of purple, white, and buff amidst the blue. The Tricolored has white head plumes, and is slightly more slender in the neck and bill than is the Little Blue.
In immature plumage, Tricolored also has a maroon neck- but a white stripe down its front makes it unlike the solidly maroon neck of a Little Blue. Young Little Blues are completely different, solid white for their first year, then adopting a "pied" plumage covered in splotches of blue and white. When white, they is easily mistaken for a Snowy Egret, but are readily distinguished with practice by the bluish-gray beak with crisp black tip, green legs (including in front), and chunkier neck and beak. Some have dusky wing tips, mainly visible in flight- these are diagnostic when present.
Tricoloreds appear more slender-bodied and longer-legged in flight, a lankiness that can distinguish them from Little Blues (with practice) even when too far away to make out the white belly.
Both species are to be expected in any of the freshwater wetlands outside the city, but the Little Blue becomes less common in saline habitats (eg, near Fourchon). Inside urban New Orleans, Tricoloreds can sometimes be found in drainage canals- I have seen them pretty regularly in the canal along Canal Street in Metairie (the short Canal Street that cuts from Oaklawn down toward the 17th Street Canal pump station). For unknown reasons, Little Blues seem to eschew the roadway canals entirely, but are frequently found in urban batture ponds and floodwaters along the Mississippi River, where they occur more often than do Tricoloreds.
I grew up on bird books in the 1970's in which the Tricolored bore its old name, the Louisiana Heron. I expect there are still those in our state who are miffed that the bird was renamed Tricolored by the American Ornithologists Union (the bird is not really three-colored anyway!).