No, that's not it unfortunately. It was a single page with a style of diagrams that shows a high-level format of something, with arrows to a zoomed-in version that details the structure of the fields. I remember its colour scheme being dominated by light blue and green, IIRC.
Very nice. The design reminds me of a website that I forgot to bookmark a long while ago, it was about explaining network protocols at the wire level, and it had some of the most amazing visuals that I ever saw. It's a shame that I forgot what it was, and googling doesn't help. If anyone knows what I'm talking about please share the link.