I tried to improve on my image of the two glasses with coloued food colouring dispersing in them; so I added a third glass. The front glass was empty, the middle glass was half full of water and the back glass was quite full.
I added red food colouring to the back glass and yellow food colouring to the middle glass.
This is a blend of two images. One of the images is back lit to show off the glass and food colouring and the second shot (taken independently) lights up the white work surface. The two images were blending in Photoshop.