Speed = -jumpStrength;

if (img.getColorAt(getX(), getY() + getImage().getHeight()/2).getGreen() > 128)

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)
import java.awt.Color;
/**
 * Write a description of class Character here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Character extends Actor
{
    private int Speed = 0;
    private int acceleration = 1;
    private boolean jumping;
    private int jumpStrength = 11;
    private int speed = 2;
    /**
     * Act - do whatever the Character wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */

    public void act() 
    {
        Movement();
        checkFall();
    }    

    public void Movement()
    {
        if (Greenfoot.isKeyDown("d"))
        {
            move(3);
        }
        if (Greenfoot.isKeyDown("a"))
        {
            move(-3);
        }   
        if (Greenfoot.isKeyDown("w") && jumping == false)
        {
            Jump();
        }
   }

    public void Jump()
    {
        Speed = Speed - jumpStrength;
        jumping = true;
        Fall();
    }

    public void Fall()
    {
        setLocation(getX(), getY() + Speed);
        if (Speed <= 9)
        {
            Speed = Speed + acceleration;
        }
        jumping = true;
    }

    public void checkFall()
    {
        Level1 level1 = getWorldOfType(Level1.class);
        GreenfootImage img = level1.getBackground();
        if (Color.GREEN.equals(img.getColorAt(getX(), getY() + getImage().getHeight()/2)))
        {
            Speed = 0;
            jumping = false;
        }
        else
        {
            Fall();
        }
    }
}