In 256208@main, we resolved webkit.org/b/247165, P3 colorspace support for WebGL canvas on macOS (and we marked GTK expectations as failing, which has since failed in WPE as well and hence failing expectations moved up to GLIB dir); In 257776@main we resolved webkit.org/b/249180, P3 colorspace support for WebGL canvas on iOS. This bug ticket is for the same functionality in GTK/WPE.
(Sorry if I added the wrong people on this bug, it may just be functionality we are missing in GTK/WPE.)