Examples: Replace Color::from_* and Color::new with palette::css where possible

[BloodStainedCrow]

As mentioned in #749, this replaces all uses of Color::from_* and Color::new with palette::css constants when possible.

This also allowed me to remove the import of peniko::Color, in all but one example project.
I do not know how to use the examples/scenes lib, so it is technically untested, but I tried to match the colors as best as possible, which should be good enough.

[BloodStainedCrow]

I stumbled onto this by trying to copy the example code into my own project, but discovered it does not compile with the vello version on crates.io.

I assume that is a known problem? If so, this is an unfortunate barrier for newcomers :(

[BloodStainedCrow]

Clippy failed because the import is only used behind the #[cfg(feature = "wgpu-profiler")] flag, which seems to not be set. Should I put the import behind a #[cfg(feature = "wgpu-profiler")]?

[DJMcNab]

Thanks for this! To use the scenes library, you should run one of the with_winit or headless examples, which both use scenes to provide their content.

I stumbled onto this by trying to copy the example code into my own project, but discovered it does not compile with the vello version on crates.io.

Hmm, I'm unsure how this change would have an impact there - the palettes used would also not be available on the release on crates.io.

main is used for development of future versions, and to see examples for a specific release, you should use that release's tag (https://github.com/linebender/vello/releases/tag/v0.3.0 for v0.3.0). Maybe it would help if we had a comment about this in our README?

Clippy failed because the import is only used behind the #[cfg(feature = "wgpu-profiler")] flag, which seems to not be set. Should I put the import behind a #[cfg(feature = "wgpu-profiler")]?

I think that's right. It's the solution we used to import Line.

[DJMcNab]

How did you find these matching colours? Were they all identical to the CSS counterpart? (if the colours have changed, the snapshot tests will need to be updated)

[BloodStainedCrow]

Oh, I did not realize the exact values of the example colours mattered for tests, so I just chose the ones from the css list, which matches most closely...

[BloodStainedCrow]

I stumbled onto this by trying to copy the example code into my own project, but discovered it does not compile with the vello version on crates.io.

Hmm, I'm unsure how this change would have an impact there - the palettes used would also not be available on the release on crates.io.

This change won´t help. I was just making sure, that the issue is known! Mentioning this in the README seems like a good idea, since many people (me included) learn a new crate by adapting it's examples.

[BloodStainedCrow]

How are the snapshot tests generated? Since they will need to be updated.

[DJMcNab]

You should use cargo nextest run to run the tests, and then follow the guidance to set the environment variable for blessing the tests which should be printed for you - you also need to have git lfs enabled.

[BloodStainedCrow]

Ah, that is what i feared. Some test pass on my machine with the modified colors (due to the leniency in the tests) and are therefore not updated, but since this introduces baseline error into each test, they now are much more sensitive, so are failing on i.e. macos.