I use the following code on http://www.diagnomics.com/
Smooth transition from b/w to color with magnifying effect (scale)
img.color_flip {
filter: url(filters.svg#grayscale); /* Firefox 3.5+ */
filter: gray; /* IE5+ */
-webkit-filter: grayscale(1); /* Webkit Nightlies & Chrome Canary */
-webkit-transition: all .5s ease-in-out;
}
img.color_flip:hover {
filter: none;
-webkit-filter: grayscale(0);
-webkit-transform: scale(1.1);
}