Changing the color button each time to press

good day members

i have a button when i press the button the color will change to black and then when i press it again it will change to yellow and then again when i press it . it will change to blue

i design the button and i gave it name in the instance name as myButton

i tried with this code ( i put the code on the time line ) . it change the color to black BUT when i tried to change it to yellow NOTHING

this is the code

button_color = new Color(_root.myButton);
_root.myButton.onPress = function() {
    if (_root.myButton!=button_color) {

any help guys

thank you