Hello!
The best way to do that is using the SetGraphicColor method on your MaterialButton, like so:
[SerializeField] private MaterialButton m_Button;
public void ChangeButtonColor()
{
m_Button.materialRipple.SetGraphicColor(MaterialColor.red500, false);
}
The first parameter is the color of the button.
The second parameter will animate (if true) or not (if false) the transition from the current color to the color you specified in the first parameter.
Have a great day ;)