Improve `Frame` API to allow picking color until after adding content… #4

Job	Run time
android	1m 29s
Check wasm32 + wasm-bindgen	4m 33s
cargo-deny aarch64-apple-darwin	43s
cargo-deny aarch64-linux-android	42s
Format + check + test	18m 25s
Check Windows	7m 0s
cargo-deny i686-pc-windows-gnu	43s
cargo-deny i686-pc-windows-msvc	38s
cargo-deny i686-unknown-linux-gnu	41s
cargo-deny wasm32-unknown-unknown	40s
cargo-deny x86_64-apple-darwin	39s
cargo-deny x86_64-pc-windows-gnu	39s
cargo-deny x86_64-pc-windows-msvc	35s
cargo-deny x86_64-unknown-linux-gnu	39s
cargo-deny x86_64-unknown-linux-musl	38s
cargo-deny x86_64-unknown-redox	40s
	39m 24s

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