Created attachment 270350 [details]
which is talking about whether 0 should be handled as 0deg.
However, it's even worse. See the examples in the attached file, where
linear-gradient(95deg, red, blue) is ok
linear-gradient(95, red, blue) is parsed with 3 colours.
smfr says there are also differences in quirks v standards mode
Implementing https://quirks.spec.whatwg.org/#the-hashless-hex-color-quirk per spec would maybe fix this.
cdumez, want to take a stab at this? :-)
Chromium passes the tests
Possibly related: bug 155874