Since my previous post and uploading the page on this subject I have noticed that the test cards look different in different browsers. In IE and Chrome the shadow card shows a just perceptible difference between the ‘4’ patch and the ‘0’ background. In Firefox, Seamonkey and Safari there is a more noticeable difference. I believe this is because these last three are implementing colour management and are showing the card ‘correctly’. This was confirmed by viewing the file in Photoshop and selecting either ‘don’t color manage’ or using the embedded profile (sRGB).
I should point out that since the page was originally uploaded I have replaced the jpeg test cards with .png files so as not to confuse matters with embedded profiles. This does not in any way invalidate the above statements but it does mean that to view the files correctly in Photoshop a profile (sRGB) should be assigned and colour management applied on opening. The appearance of the test cards (now without embedded profiles) in the listed browsers is unchanged, suggesting that those browsers implementing colour management are assuming an sRGB profile.