Why are Chelsea wearing yellow kit in FA Cup final vs Liverpool & why isn't Havertz in the squad?

Chelsea sprang two surprises on Saturday ahead of their FA Cup final meeting with Liverpool at Wembley.
The Blues raised a few eyebrows in foresaking their usual colours in favour of a yellow kit.
There was also a notable absentee in the Chelsea ranks as Kai Havertz was omitted from the matchday squad to take on Jurgen Klopp's charges.
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Why are Chelsea wearing yellow in FA Cup final vs Liverpool?
While there is no stated reason behind the kit change on Chelsea's part, superstition may have weighed heavily in the decision.
Chelsea have won several titles playing in yellow shirts, including the 2009 FA Cup over Everton.
Manager Thomas Tuchel vowed to ITV before the game: "We will win in yellow."
Why isn't Havertz playing for Chelsea?
Tuchel also revealed that a niggling hamstring injury has prevented Havertz from joining the Blues squad for Saturday's showpiece fixture.
"We tried until the last minute. He has hamstring problems," he explained.
"Not a real injury. He feels if he goes, there will be an injury.
"If he says this in front of a final it is serious enough to not start. He puts in a lot of sprints, intensity runs. We cannot risk this."