In the latest build (8.1.2007) the resource.columns[] array supports .backColor and .cssClass properties (in addition to .html).
Example:
dp.resources = [
{ name: "Room 101", id: "101", columns: [{html: "Floor 1", backColor: "#ccc"}, {html: "2 beds", cssClass: "highlight" }] },
{ name: "Room 102", id: "102", columns: [{html: "Floor 1"}, {html: "3 beds"}] },
{ name: "Room 103", id: "103", columns: [{html: "Floor 1"}, {html: "1 bed"}] },
{ name: "Room 201", id: "201", columns: [{html: "Floor 2"}, {html: "2 beds"}] }
];
You can also reach the column data in onBeforeResHeaderRender using args.resource.columns[]:
https://api.daypilot.org/daypilot-scheduler-onbeforeresheaderrender/
You can download the latest build in the sandbox:
http://javascript.daypilot.org/sandbox/