[R] modify rectangle color from image

[Saurav Pathak]

Hi,

I need some suggestion on how I could modify the color on some
rectangle that I have created using "image".

In other words, I have a 5x5 matrix, say, m.  

        m <- matrix(rnorm(25), nrow=5)

I create a grid of rectangles by:

        image(m)

Now I want to change the color of rectangle (3,3) to blue. 

I don't know how this could be done, and searching the web has given
me no hint.  

Thanks for your help.

-- 
saurav