I don't understand how you determine which counties in Texas or Colorado are "county" school districts. I think you are applying a Georgia or Florida concept to places where it is an alien concept.
It's not a perfect concept obviously. Frankly, as I moved west, it was frustrating to not have a simple metric by which to match up each county with a district, which is why I had to then start using a third color for counties that didn't even have one school district that was easily identifiable with a county.
In Texas, all I could do without losing sanity was match up the districts that shared a name with a county (roughly half of the counties). It appeared that there are districts that covered unincorporated areas of an entire county, as well as municipal districts (and maybe some that cover multiple counties?), that were all essentially "incorporated school districts". It was definitely a lot simpler along the Atlantic and the Gulf to do this.
The problem is that in some cases it happens to be that the name of the county and a city or town in the county have the same name, but the school district is named for the town. And there are lots of cities and towns in Texas that are not in the county of the same name.
ISD stands for "Independent School District", and in particular that they are independent of the county government. Texas was a very rural state until the 20th century. So you would have to have a school within walking distance (or perhaps horseback riding) distance for elementary school children. But there might not be enough farmers or ranchers to support a school board. There would be a one-room or two-room schoolhouse, and a couple of teachers. But the administration would be by the county school board. The county seat might have a high school, and more gifted children might board in town during the week to attend the high school. Larger towns might form an Independent School District which they would provide funding. The smaller schools were common schools.
Around the 1940s school districts began to be consolidated. I found a history for the North Lamar ISD that showed that 44 districts were included (there were several levels of consolidations). North Lamar covers about half of Lamar County).
Because school districts were originally created by county school boards, there is usually some conformance with county boundaries. But consolidations may have occurred across lines, and some boundaries may have been adjusted to match roads. Consolidation occurred after there were roads and vehicles to take students to and from school each day.
Sherman County is in northern tier of the panhandle. Sherman ISD (Grayson County) is north of Dallas.
Ochiltree County and Perryton ISD are roughly the same.
Hemphill County is in the panhandle. Hemphill ISD is in extreme Deep East Texas (Sabine County)
Hemphill County and Canadian ISD are roughly the same.
Roberts County and Miami ISD are roughly the same.
Moore County and Dumas ISD are roughly the same.
Hartley ISD is a relatively small district in Hartley County. A case could be made that Dalhart ISD is a bi-county district in terms of students. Dalhart is the county seat of Dallam County, but not Hartley County (neither is Hartley). The county seat is Channing, which was one of the HQ of the XIT Ranch. Incidentally, Dalhart is closer to Santa Fe, Denver, Oklahoma City, Topeka, Cheyenne, and Lincoln, than it is to Austin.
Wheeler ISD is just of several school districts in Wheeler County. Shamrock is slightly larger than the town of Wheeler (Shamrock is on the interstate).
Collingsworth County and Wellington ISD are roughly the same.
Armstrong County and Claude ISD are roughly the same.
Childress County and Childress ISD are roughly the same, though the ISD is named after the town.
Hale Center is near the center of Hale County, but the county seat is in Plainview which has about 10 times the population. Hale Center ISD is just one of several districts in the county.
Floyd County and Floydada ISD are roughly the same. Floydada was originally Floyd City, but the name was changed to avoid confusion with another Floyd, TX (in Hunt County). The origin of the "ada" is uncertain.
Motley County and Motley County ISD are roughly the same. The town of Matador has more than half the county population. It may just be happenstance that the school district is named after the county rather the town, or perhaps smaller communities resisted submerging their identity to that of a rival community. The athletic teams are known as the Matadors.
Cottle County and Paducah ISD are roughly the same.
King County and Guthrie ISD are roughly the same.
Lubbock ISD is named after the city, and is just one of several districts in Lubbock County. Several of the districts are of moderate size due to population spillover.
Yoakum County is west of Lubbock. Yoakum ISD is between Victoria and San Antonio. Yoakum, TX is named for Benjamin Franklin Yoakum the nephew of the namesake of Yoakum County, Henderson King Yoakum.
Garza County and Post ISD are roughly the same.
Kent County and Jayton-Girard ISD are roughly the same.
Stonewall County and Aspermont ISD are roughly the same.
Scurry County is between Abilene and Lubbock. Scurry-Rosser ISD is in Kaufman County east of Dallas. They are named for different Scurry's (and one is named after the first name, and the other after the last name.
Borden County and Borden County ISD are roughly the same.
There are two Dawson ISD's. One is in the northwest corner of Dawson County, between Big Spring and Lubbock. It is based in the town of Welch. The county seat is the much larger town of Lamesa (pronounced with a long e), roughly 40x the size of Welch. I could find no explanation of why the small ISD in a corner of the county has the name of the county. The other Dawson ISD is in Navarro County (pronounce Na-vair) southeast of Corsicana, and is based on the town of Dawson.
Gaines County and Seminole ISD are roughly the same, particularly when population is considered.
Andrews County and Andrews ISD are coterminous. The ISD is named after the county seat, which has 6/7 of the county population.
El Paso ISD is named after the city. It is just one of several in the county. Ysleta ISD is also quite large.
Culberson County and Culberson County-Allemore ISD are roughly the same. Until recently, Allemore ISD was the smallest in the state, and there would be an occasional story showing a girl on a swing, who constituted the third grade class, and fourth grad etc.
Presidio ISD is named after the city. The bulk of Presidio County is in Marfa ISD, though most of students are in Presidio ISD.
Terlingua Common School District in Brewster County, west of Big Bend National Park, is one of the few remaining common school districts in the state. Oddly, it operates a high school, which is attended by students from neighboring San Vicente ISD. Historically, ISDs developed because the towns were willing to be taxed to support a high school. Some of the initial consolidations were to create rural high school districts.
The city of Pecos is in Reeves County, the county to the northwest of Pecos County. Reeves County and Pecos-Barstow-Toyah ISD are largely the same, though Barstow is neigboring Ward County.
Terrell County and Terrell County ISD are coterminous.
Wink-Loving ISD includes all of Loving County. Wink is named after Winkler County (the name was truncated to satisfy postal authorities). But the county seat and much larger town in Winkler County is Kermit, which is served by Kermit ISD. Loving County is the only county in Texas without any school districts headquartered in the county, and has no schools. Any children are bussed from Mentone to Wink.
Monahans-Wickett-Pyote ISD includes much of the area of Ward County, and most of the students.
Crane County and Crane ISD are coterminous. Crane is the county seat and has about 2/3 of the county population.
Reagan County and Reagan County ISD are coterminous.