Disgusting as it may be to you, Sadler, I'm afraid that the U.S. games did have color shade variations according to genre and I can't help but have an eye for accuracy even if the various shades do become confusing at times.
I did a quick image search on Gunboat's box and the banner is butterscotch-orange or cantaloupe as your color graph defines it.
There are also a few game releases who's color codes were incorrect like Chase H.Q., Fantasy Zone, Hit the Ice and more that were arcade titles that somehow ended up under "Sports", "Driving", "shooting" and etc.
Those ones should have been color coded Hot-Pink or mara-whatever-o.