Default color types to opaque white

[waywardmonkeys]

We choose an opaque color because otherwise the OpaqueColor would have a substantially different default value than the other color types.

White is the same as the default color within bevy_color.

The default color is used by the Brush in Parley and likely other places.

[raphlinus]

I'm ok with this, though I believe the canonical default is mediumorchid.

[waywardmonkeys]

I'm going to keep this approval in my pocket for now and see if we can avoid needing it! :)

[DJMcNab]

In our current world without rust-lang/rust#132162 on stable, I think having this is fine. I'd personally still advocate for a vile default, so that users can notice not overriding it, but not enough to block the "safe" white.

[tomcur]

Doing a vile default is a little bit tricky, and may require specifying the color on the color space: doing a conversion at runtime from some vile color in a specific color space is quite a bit of operations for a color that is likely to be overwritten, and it may fall outside that color space's natural gamut, making it a bit messy.

[waywardmonkeys]

Many color libraries don’t provide a default… I am fixing the things that need it for now and my inclination is to only merge this under duress.

[waywardmonkeys]

Converting to draft as there is no intent to merge at this time.

[waywardmonkeys]

I hope to never need this.