So let's say that gets pushed through and the state is split. The state of Colorado will need a new name, perhaps Columbine after a frequently used nickname (one that maybe won't pick up unfortunate implications in the future since the high school in question probably would refrain from using it.)
Ultimately the two states would grow apart culturally but end up bein similar in many ways - like other west coast states, it would be fairly left-wing, with California itself being much like Oregon or Washington and Colorado walking a line between being about Hollywood culture and being the tough-on-crime three-strikes state. Interestingly, California may oppose a guy like Reagan, since he would be seen as a Coloradan.
Also, the demographics would change quite a bit with two decent-sized but not huge states. Two more Senators would go to Washington (and would there be a fight to keep the number of states at 50 or would pushing it to 51 spur addition beyond that?) This puts the number of EC reps at 540, a small change but one that perhaps would make a difference especially in a squeaker of a contest such as Bush-Gore in 2000. In that case, one measly elector thinking the decision is bogus would throw the election to the House. Or if there's another state, say, Puerto Rico, added before 2000 and it brings the numbers to 542, if PR goes blue, that probably hands the election to Gore, altering American policy after 9/11.
Another fun one goes back to if VA stays Union, perhaps under Lincoln's influence. That means no West Virginia and DC stays nestled in Union territory. Alternatively if MD splits off despite Lincoln's best efforts, we probably have a new capital.