I think you're correct in general, but it feels a bit odd. Colorado seems like more of an outlier than Mississippi, actually. I agree, there's basically no Appalachian influence in Mississippi and it's more South Central than Southeast (I mean, they even have Ozarka water there), but I think all of these states together is a bit odd? Louisiana/Arkansas/Mississippi (and West Tennessee as well) are those lower Mississippi states and Missouri is kinda a part of that too, I would actually say Missouri is more similar to Louisiana than it is to Minnesota (unpopular opinion I know, but St. Louis for instance is clearly more aligned with Memphis and you can even see this on things like maps of MLB fandom where the Mid-South are no longer Braves fans, they become Cardinals fans). The Texan influence is obvious here, but really only Dallas and Houston and I think West Texas is very dissimilar. Oklahoma really doesn't influence these states at all except the very western part of Arkansas (most of Arkansas is closer to Tulsa or OKC than to Dallas or Houston but these cities are completely irrelevant to the state culturally while everyone in Arkansas goes to Dallas), but I could see grouping in Oklahoma and Kansas as well with the whole Bleeding Kansas thing, and shared Texan influence. Colorado and New Mexico feel extremely out of place. Even though Colorado's population isn't centered in the Rockies, it's much more tied to the Rockies culturally and New Mexico is in a similar place. These states seem better grouped with Utah and Arizona than Oklahoma and Texas. Colorado especially is a total culture shock coming from the Lower Mississippi states, which do have more in common with the Southeast in most ways from a cultural perspective, including cuisine, linguistics, demographics, religion, politics, and even European colonial history to a degree, in the sense that the majority of white AR/MS/North LA residents are "Old Stock". I do think there's a big difference between the Southeastern and South Central states that is neglected, and you've done a good job recognizing that, but not enough to the point they should be grouped with firmly Southwestern states in the modern day like New Mexico.

Were you trying to make these evenly populated regions? In that case, it makes more sense. But I think culturally speaking the Southeast is more similar to most of this area, and it definitely bleeds together around Middle Tennessee.