There is no method available that can help us to change the color of NumberAxis labels, there is a method called setTickLabelFill to change the color of tick labels but there is no method like setLabelFill. In Javafx version 1.3 this was achievable by using the labelFill property like this

xAxis: NumberAxis {
                    lowerBound: 260
                    upperBound: 320
                    tickUnit: 10
                    label: "Center of Gravity (inches from datum)"
                    tickLabelFill: Color.WHITE
                    labelFill: Color.BLUE
                }