How can i detect Squire and Circle objects in image?

My project is about detecting color and shapes, And i have two shapes (Circle and Squire).How can i detect the shape in this case. And after that extract the color of the shape? Like this image for example

[KSSV]

Attach an image as an example....

[odai kiwan]

Like this one for example

Answer 1

[KSSV]

I = imread('circle.jpg') ;
I1 = im2bw(I) ;

[y,x] = find(I1~=1) ;

c = mean([x y]) ;

R = max(sqrt((c(1)-x).^2+(c(2)-y).^2)) ;

th = linspace(0,2*pi) ;

xc = c(1)+R*cos(th) ;
yc = c(2)+R*sin(th) ;

imshow(I) ;
hold on
plot(xc,yc,'r')

[odai kiwan]

Thanks man!! And how i can extract whats the color in the circle??