The first three are one-digit, two-digit and three-digit signs that can be used for state highways of primary importance. The tourist-friendly colors used are azure blue and tropical sea green.
The grey fields represent sky, i.e., the signs are cut-out shapes, not rectangles.
Here we have a state secondary classification and I chose coral red, bright red, dull gold and white with a black border.
And at last we have the county roads ("Pasco" is misspelled. Sorry.) I have a two-tone blue, warning sign Spanish orange, and goldfinch yellow for better visibility especially at night, although Spanish orange is okay in full sunlight.
Come to think of it, white letters with black outline would work better on the primary state route markers above, too.