I don't remember the exact suit, but I think in the 90's/early 2000s, it was a pretty bad-looking suit. Still, this scene doesn't sound very funny...
In this context, the suit "making a point" means that the suit is acting as a symbol for Ross' freedom to do as he pleases now that he is no longer dating Rachel. When Ross agrees, then Rachel turns that statement around on Ross by telling him he is "free to look as stupid as [he likes]." Synonym phrases would be "So the suit is making a statement" or "So the suit is a symbol."
All 3 of the other references (the riverboat/Colonel Sanders/cotton gin) evoke the image of a Southerner. In the United States, wealthy white men in the 1800s and very early 1900s would sometimes wear light-colored linen suits. This was a sign of their wealth for having the fabric clean and crisp, and also kept them cool in the humid heat (the Southeastern US is very humid all year long) as the sun would reflect from the light-colored fabrics. It later became a tacky uniform for some people in work like guiding riverboats. There has been a cultural divide between the Yankee northern mentality and the South since at least the Civil War era, so making fun of Southerners goes along with the "cosmopolitan" New Yorker image of Friends.
Colonel Sanders was not a military colonel, but a "Kentucky Colonel," which is just an honorary title that the governor of the state of Kentucky can give to anybody they want... some governor chose to give it to Sanders because of his good Kentucky-style cooking.
Eli Whitney invented the cotton gin. I don't think he wore white suits, but again, it just fits with the Southerner-image joke. The cotton gin is a mechanical machine that could separate cotton bolls from their seed, which really increased efficiency when turning cotton into fabric. People say that America rose to greatness because of the cotton gin, which helped propel the US into the industrial revolution.