addFillNode = function () {
					// Add the fill subnode. When colors attribute is used, the meanings of opacity and o:opacity2
					// are reversed.
					markup = ['<fill colors="' + colors.join(',') + '" opacity="', opacity2, '" o:opacity2="', opacity1,
						'" type="', fillType, '" ', fillAttr, 'focus="100%" method="any" />'];
					createElement(renderer.prepVML(markup), null, null, elem);
				}
Take a color and return it if it's a string, make it a gradient if it's a
gradient configuration object, and apply opacity.

@param {Object} color The color or config object