Sets the colour of the dropdown background pane.
background
Examples
const dropdown1 = $.makeDropdown($.w/2, 30, 100, [
"Option A",
"Option B",
"Option C"
]);
const dropdown2 = $.makeDropdown( $.w/2, 80, 100, [
"Option X",
"Option Y",
"Option Z"
]);
function update() {
dropdown1.background = "orange";
dropdown2.background = "rgb(75, 15, 255)";
dropdown1.draw();
dropdown2.draw();
}