In the US, there is no standardized color coding of anything at gas stations or even truck stops. Even the fuel fills for the fuel delivery transports are not standardized by color code. With in companies there might be standardized color codes, but you can not even depend on that if the station is independently owned.
Mobil, BP, ARCO, Shell, Chevron all have their own color coding going on, so always read what it says on the pump!!!
Here is the API "recommended" color coding for bulk plants (tank farms):
"(1) Gasoline—unleaded:
(a) Highest grade (octane)—red circle with white cross,
(b) Mid-grade (octane)—blue circle with white cross,
(c) Lowest grade (octane)—white circle with black cross;
(2) Vapor recovery—orange circle;
(3) Diesel fuel (low sulfur)—yellow hexagon;
(4) Diesel fuel (high sulfur)—yellow hexagon with blue stripe;
(5) No. 1 fuel oil (low sulfur)—purple hexagon with yellow stripe;
(6) No. 1 fuel oil (high sulfur)—purple hexagon with yellow and blue stripes;
(7) No. 2 fuel oil (low sulfur)—green hexagon;
(8) No. 2 fuel oil (high sulfur)—green hexagon with blue stripe;
(9) Kerosene (1-K low sulfur)—brown hexagon;
(10) Kerosene (2-K high sulfur)—brown hexagon with blue stripe;
(11) Monitoring or test pipes—white circle with black triangle and the words, "Monitoring Pipe—DO NOT FILL"."
You should note that ULSD is a yellow hexagon while #2 fuel oil (heating oil) is a green hexagon. But you can not even depend on this, as it is only recommended , but not required!!!