Top speed limits in the United States; lightest red color (Hawaii) is 60 mph, darkest green color (certain counties in Texas) is 80 mph.
Entire state is one color if the top speed limit is broadly applicable. States may be graphically split into regions if different top speed limits exist in substantially-sized regions (generally larger than urban areas).
From Blank_US_Map.svg (by Wikicommons user Theshibboleth) and Texas county map, also available on Wikipedia.

Map colored by Shadowlink1014 and novasource.
Transferred from en.wikipedia to Commons.
Shadowlink1014 at English Wikipedia

Later versions were uploaded by Novasource at en.wikipedia.