More compact `Debug` formatting of `Color32` #12844

Job	Run time
cargo-deny aarch64-apple-darwin	37s
cargo-deny aarch64-linux-android	37s
Check wasm32 + wasm-bindgen	2m 31s
Check wasm32+atomics	1m 32s
cargo-deny i686-pc-windows-gnu	36s
cargo-deny i686-pc-windows-msvc	40s
Format + check + test	16m 51s
cargo-deny i686-unknown-linux-gnu	36s
cargo-deny wasm32-unknown-unknown	35s
android	23s
cargo-deny x86_64-apple-darwin	37s
cargo-deny x86_64-pc-windows-gnu	35s
cargo-deny x86_64-pc-windows-msvc	34s
ios	21s
cargo-deny x86_64-unknown-linux-gnu	37s
cargo-deny x86_64-unknown-linux-musl	39s
cargo-deny x86_64-unknown-redox	40s
Check Windows	1m 59s
	31m 0s

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