The proposed new MUTCD requires green for enhanced mile markers (the current MUTCD is that either green or blue can be used, but the same agency [state, local, etc] has to use one color for all their enhanced mile markers)
Do states with blue enhanced MMs use regular MMs (which have to be green)? That would seem to be a remarkable change when a motorist starts seeing blue MMs after having seen green ones along the route.
In Ohio, yes. The state only uses green regular integer mile markers on the right side on rural interstates, and the blue enhanced mile markers (generally in intervals of 0.2, exception is Cincinnati with 0.1) start appearing in the median in urban/suburban areas, along with the green regular ones. So at whole miles in a city, you see, for example, a blue “North (75) Mile 10.0” in the median, as well as a standard “Mile 10” with stacked digits on the right.
Kentucky is similar to Ohio in terms of how mile markers are done, so they have both at integer miles when enhanced mile markers are used too.
In Indiana, the green regular mile markers aren’t used when enhanced mile markers (in intervals of 0.1, also placed in the median) are used in the urban areas. In rural areas, the green regular mile markers are used every 0.5 miles.
I drove through Tennessee a month ago, and iirc, don’t think I saw regular mile markers when enhanced ones are used. Though you might know about TN’s practices more, as one of your border states.