Hi @Abhi, this is certainly possible with a bit of Jquery or simple CSS. You could alter the custom module to have two different image fields, one that holds the grayscale image and one that holds the normal image. You can then hide one and show the other depending on if the user is hovering or not. This stackoverflow thread goes over how to do this.
Another option would be to have a tinted overlay over the images, and then remove this overlay on hover