The two rows should look identical in browsers that handle transparency correctly. In a normal image viewer (one with no preferred background, i.e., not a web browser), the top four icons should have backgrounds of yellow, white, gray and black, respectively; this will be visible on the left sides of all four images and around the periphery of the first and third icons (the two `X' images). The icons in the bottom row will generally default to a black background in non-browser image viewers.
All six columns will look essentially identical (not counting the printed numbers) if your browser does gamma correction. Within each icon, the two rightmost bars (one solid color and one with alternating black and max-intensity horizontal lines) will appear to be approximately the same color, assuming your browser's gamma correction is correct for your monitor. If your browser just dumps the raw pixel data on screen, the icons to the left will have darker bars than those to the right.
