please how can i write a code for an actor to change colour after a few seconds, dont know how the timer works
You only need a timer field:
private int colourTimer;
public void act()
{
if (colourTimer < 150 && ++colourTimer == 150) changeColour();
}
You can then add a changeColour method which does the actual changing of the colour or you can replace that method call on line 5 with a block of code that does it right there.