Document our encoding of Color datatype and component (#3289)

### What
* Related to #2782

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested [demo.rerun.io](https://demo.rerun.io/pr/3289) (if
applicable)

- [PR Build Summary](https://build.rerun.io/pr/3289)
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crates/re_types/definitions/rerun/components/color.fbs

@@ -9,7 +9,10 @@ namespace rerun.components;
 
 // ---
 
-/// An RGBA color tuple with unmultiplied/separate alpha, in sRGB gamma space with linear alpha.
+/// An RGBA color with unmultiplied/separate alpha, in sRGB gamma space with linear alpha.
+///
+/// The color is stored as a 32-bit integer, where the most significant
+/// byte is `R` and the least significant byte is `A`.
 ///
 /// \py Float colors are assumed to be in 0-1 gamma sRGB space.
 /// \py All other colors are assumed to be in 0-255 gamma sRGB space.

crates/re_types/definitions/rerun/datatypes/color.fbs

@@ -8,7 +8,10 @@ namespace rerun.datatypes;
 
 // ---
 
-/// An RGBA color tuple with unmultiplied/separate alpha, in sRGB gamma space with linear alpha.
+/// An RGBA color with unmultiplied/separate alpha, in sRGB gamma space with linear alpha.
+///
+/// The color is stored as a 32-bit integer, where the most significant
+/// byte is `R` and the least significant byte is `A`.
 ///
 /// \py Float colors are assumed to be in 0-1 gamma sRGB space.
 /// \py All other colors are assumed to be in 0-255 gamma sRGB space.