Detecting Particular line and circle.

Hi guys this is my code. my task is to detect white line in green field and yellow goal post and orange ball. I am unable to detect the ball and yellow line and it is detecting all white line. i just want green field white line should get detected and yellow goal post and orange ball. PLEASE HELP ME THANK YOU.

imread ('C:\Users\new\Desktop\Ass1\robocup_image1.jpeg');

img =  imread ('C:\Users\new\Desktop\Ass1\robocup_image1.jpeg');

imshow (img);

RGB = imread ('C:\Users\new\Desktop\Ass1\robocup_image1.jpeg');

imshow (RGB);

I = rgb2gray(RGB);
imshow(I)

BW = edge(I,'Canny');

imshow(BW)

[H,theta,rho] = hough(BW);

figure, imshow(imadjust(mat2gray(H)),[],'XData',theta,'YData',rho,...
        'InitialMagnification','fit');

xlabel('\theta (degrees)'), ylabel('\rho');
axis on, axis normal, hold on;
colormap(hot)

P = houghpeaks(H,5,'threshold',ceil(0.3*max(H(:))));

x = theta(P(:,2));
y = rho(P(:,1));
plot(x,y,'s','color','black');

lines = houghlines(BW,theta,rho,P,'FillGap',5,'MinLength',7);

figure, imshow(BW), hold on
max_len = 0;
for k = 1:length(lines)
   xy = [lines(k).point1; lines(k).point2];
   plot(xy(:,1),xy(:,2),'LineWidth',2,'Color','green');

     % Plot beginnings and ends of lines
     plot(xy(1,1),xy(1,2),'x','LineWidth',2,'Color','yellow');
     plot(xy(2,1),xy(2,2),'x','LineWidth',2,'Color','red');

     % Determine the endpoints of the longest line segment
     len = norm(lines(k).point1 - lines(k).point2);
     if ( len > max_len)
        max_len = len;
        xy_long = xy;
     end
  end

Answer 1

[Image Analyst]

See my color segmentation routines in my File Exchange http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862

In addition see attachment where I track a green Sharpie marker.