The new Speed Index metric is great addition to WPT. I am having a question on the value of the index. Since it's calculated using histogram value of each video frames, will a site's color scheme affect it's Speed Index value ?
Maybe yes, maybe no. A background color or image will cause a change in the % of the screen that is complete but it largely depends on how much of that background is left unobstructed in the final UI.
Something like the Google landing page would be a lot more susceptible to that (if it had a background color) because there's almost no content that overlays. A portal page that puts a lot of content on top of a background color will not because the background color is not the final state for most of the screen.
It will be interesting to test it against an increasing corpus to see how well it holds up but so far it has performed a lot better than anything else I tried.
One of the things I want to set up is a "hot or not" site that plays videos of arbitrary pages loading side by side and asks people which felt faster and then correlate that to the calculated speed index scores to see how it holds up.