UI: don't multiply color channels by alpha #39005

Job	Run time
check-doc	7m 25s
miri	6m 6s
ci	2m 9s
build (windows-latest)	3m 51s
build (ubuntu-latest)	2m 15s
run-examples-macos-metal	5m 5s
toml	1m 57s
build (macos-latest)	3m 4s
typos	6s
check-bevy-internal-imports	3s
check-cfg	1m 38s
check-missing-examples-in-docs	33s
check-missing-features-in-docs	44s
markdownlint	1m 12s
check-compiles	3m 4s
msrv	50s
build-wasm	41s
	40m 43s

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