Mini-rant by Suzie Stick-in-the-Mud: I realize that when people say that a certain color, like red or denim blue, is "a neutral for me" they just mean that they're willing to mix it with any other color, or that they find it versatile, or that it complements much of their wardrobe, but I'm not a huge fan of talking about colors found on the color wheel as neutrals. By definition, they're not.
If it sounds like I'm being sour, rest assured that I'm with you, Carter. Very dark jeans with black don't look right to me either. I think it's because they're an almost-match, rather than because either of them is neutral.
Almost any very close color pairing looks off. I love brown with black, but super-deep chocolate browns with black definitely make it look like you got dressed in the dark. You need a more "colorful" brown to make it work. Same with "true navy" (the kind you have to take over to the window to see if it's black or not) -- the blue has to be easily, visibly different from the black to look intentional.
Almost-matched color combinations are neither one thing nor another: they lack the drama of head-to-toe matching, and they lack the visual interest of contrast.
Am I making sense? I'm hoping that Jean (Greenglove), our veteran artist and teacher and brilliant grasper of what does and doesn't work in color, will chime in.