This may describe it better.
http://www.mcmurrayhatchery.com/product/speckled_sussex.html
The little thumbnail paintings on the MM site are the pictures out of the Standard of Perfection. They don't use photos, but idealized renderings of what the Standard calls for. Unfortunately, being a copyrighted book, you only find very small thumbnails. If you get the actual book, it may be easier to tell what I'm saying.
Do you see on the wings how there are two parallel lines of speckles? Also on the upper body & neck, there should be hardly any white. Along the body and up to the tail, the speckles should be random but somewhat equally spaced.
If you look at the photos people post of their "pretty" speckled sussex, they are sometimes entirely white along the neck and body. People tend to prize the birds with the most 'porcelain' showing, not realizing that it should only be present in moderation.
Oh, and by the way, I really do love the color on my SS's... but, I have to be honest, the specimins I've seen at Fairs in England are so much larger than here in the US. Over there, the Light Sussex is very common and bred to a massive size (great for backyard cross breeding). I think in general, in the US, the hatcheries have got hold of the Sussex's and outcrossed them with Leghorns and RIR's to improve laying over the generations. It shows as it just seems to me our Sussex are just too small.