My wife and I live in Grand Lake. There are two forest service campgrounds with electric at Lake Granby and at Shadow Mountain Lake both are on the lake and are nice. They fill up on weekends but you can drive in and get a site midweek. If you come in without reservations in the weekend, you might find a space in one of the two commercial campgrounds in Grand Lake or there is lots of free, no services, camping up County Road 4.
Not to knock Grand Lake but our favorite place in the state to camp is Steamboat Lake State Park north of Clark. Most sites have electric. You can usually drive in middle of the week and get a site but weekends book up and you may have to settle for a non electric site at that time.
We like it because of Steamboat and Pearl Lakes, lots of nearby forest hiking and biking, and its closeness to Clark and Steamboat Springs. There is pretty good fishing and lots of birds including Sand Hill Cranes.
Our second favorite is a KOA near Gould, (Walden). It is near the Colorado State Forest and is quite remote. Hiking and biking at new places is limitless. It has full hookups.
The state parks in Colorado are good bets as they generally have sites with water and electricity. You can book reservations on the internet.
If you want to make a trip of just Colorado, you can do it and not be bored. We have lived here all our lives and are still finding new places to stay. Last year we went to Grand Mesa (near Grand Junction) and stayed at a nice forest service campground with electric and water and on Blue Mesa Reservoir near Gunnison with another government campground with electric and water.
Some of the campgrounds recommended by other posters are new to us and we will save them for future visits.
We have a Honda generator and feel no hardship whatever camping in a site with no services. If you are prepared to boondock, there are thousands of places to stay.