Haw. Code R. § 13-241-1
As used in this chapter, unless otherwise provided or the context clearly indicates otherwise:
"Background" means the portion of the hull or superstructure, or a specially provided backing plate, upon which displayed numbers are placed, but shall not include any border, trim, outlining or shading of the numerals or letters.
"Block characters of good proportion" means numerals and letters that are vertical, not slanted, and of a plain style, not script or of varying thickness and preferably without border, trim, outlining or shading. Border, trim, outlining, or shading of characters shall be disregarded in determining height of the character, or its style or color contrast. Numerals and letters shall be of one solid color exclusive of any colored border, trim, outlining or shading which will form a good contrast with the color of the background and so maintained as to be clearly visible and legible.
"Contrast with the color of the background" means that numerals and letters in a displayed number is of such a different color from that of the background as to be distinctly visible and legible.
Haw. Code R. § 13-241-1