Correlation, but not perfect. Largely because most of the Union stayed, so you get states like North Dakota that was part of a Union territory but a red state. That and Appalachia (e.g. West Virginia, Ohio) swung pretty hard from the union cause to the confederates thanks to coal baron propaganda and the erosion of union power in the post Regan era. The confederate states are almost all red though, with the only current exception being Virginia and varying degrees of hope for near future conversions in Georgia, North Carolina, and Texas