I'm not talking Octoling costume colors, I'm talking ink colors.
@MoonlitIllusion did bring up a good point about colors, but I'm still skeptical.
While Rex may have concept art dating back to 2014, his game didn't come out until much later, and Sakurai would likely add Elma, the main character of the released and successful Xenoblade Chronicles X, instead of the unproved Rex, who's game wouldn't come out until much later.
Also I feel like Spring Man wouldn't be added late like Sonic as Sonic was a very special case. Unless Nintendo directly came in and said "add Spring Man," which I highly doubt they would as they let Sakurai do his own thing, he likely won't be in the base game.
In other news, another s***ty 4chan leak appears.