transition(effect, color, duration) {
		if (effect === "fade") {
			_fade.color = color;
			_fade.duration = duration;
		}
	}
specify a global transition effect
@name transition
@memberof state
@public
@param {string} effect - (only "fade" is supported for now)
@param {Color|string} color - a CSS color value
@param {number} [duration=1000] - expressed in milliseconds