Those are my old stomping grounds. Last year I did almost that same route in reverse, from Colby to the Lexington area. Those are all decent hiways, nothing too fancy or poorly maintained. It's thru a very rural area, but what is nice is not a lot of traffic. But be careful, there may be 3 hills between Lex and Colby.
I assume you'll catch I-70 at Colby to take to Colorado. Watch for strong south winds on that E-W hiway thru western Kansas. It makes driving a tall moho a challenge. You have to steer slightly into the wind to keep the rig going straight. This is fine until you cross under one of the many underpasses that block the wind. You will soon learn to let the steering wheel go straight in the underpass and again turn slightly into the wind as you transition out of the underpass shelter effect. Kind of hard to explain, but if it's windy you'll soon know what I mean. Have a great trip!