How to identify color and shape of blobs in an image

Hi..I am a beginner to matlab.Am working on a project. Suppose there is an image which consists of a no. of basic shapes(triangle,rectangle etc.) of Red,green or blue color. I want to detect the color,shape and centroids of those shapes in that single image by processing the image. And then connect the centroids of the blobs by straight lines. Can tell me any way how to do it?? Please help!! Thanx in advance. The image file is provided for help.