Added documentation for optional color configurations on Android.

[bbusenius]

This PR is to add documentation for the new color settings added to briefcase-android-gradle-template in PR #77. The new color settings are:

accent_color
primary_color
primary_color_dark

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[bbusenius]

I took a stab at writing a newsfragment. I hope that wasn't too audacious. I wasn't sure if that minuscule work should rise to the level of a feature but since it's new functionality, that was my best guess. Let me know if you want me to change anything.

[freakboy3742]

Looks good! This definitely qualifies as a "feature" to my mind - it's a notable capability that now exists that didn't previously.

A couple of review suggestions inline; it's probably also worth moving the Android-specific notes to the Android configuration guide. That document already mentions splash_background_color; it would make sense to me to expand that section to clarify how the other app colors will be applied.

[freakboy3742]

Even though it's currently Android-only, the feature is a generic configuration item, so it should be framed in those terms.

Suggested change

	Briefcase Android Gradle Template now allows for setting accent_color, primary_color and primary_color_dark. These settings can now be used in pyproject.toml for Android projects.
	Apps can now specify a primary color (for both light and dark modes), and an accent color. If the platform allows apps to customize color use, these colors will be used to style the app's presentation.

[bbusenius]

I see, yes, that makes perfect sense.

[freakboy3742]

Notes about the specific platform interpretations should be in the relevant platform guide, unless they're indicative of behavior on all platforms.

Suggested change

	A hexadecimal RGB color value (e.g., ``#008577``) to use as the primary color
	for the application. On Android this will be used to color the app bar in the
	main window. This setting is only used if the platform allows color
	modification, otherwise it is ignored.
	A hexadecimal RGB color value (e.g., ``#008577``) to use as the primary color
	for the application. This setting is only used if the platform allows color
	modification, otherwise it is ignored.

[freakboy3742]

As above

Suggested change

	A hexadecimal RGB color value (e.g., ``#008577``) used alongside the primary
	color. On Android this is used to color the status bar at the top of the
	screen. This setting is only used if the platform allows color modification,
	otherwise it is ignored.
	A hexadecimal RGB color value (e.g., ``#008577``) used alongside the primary
	color. This setting is only used if the platform allows color modification,
	otherwise it is ignored.

[bbusenius]

That all makes sense. I made the suggested changes and moved the Android specific language to the Android configuration section of docs/reference/platforms/android/gradle.rst. Feel free to let me know if there's anything else you want me to change.

[freakboy3742]

Sorry - I should have been clearer; this section is for settings that are unique to Android configuration. I was referring to adding a note up around L100, where there's already a mention of how splash_background_color will be interpreted.

[bbusenius]

I see it now. Your instructions were fine. I think it just threw me that it was in the Splash Image format section. I created a new section there for colors and added another mention of splash_background_color to be consistent and comprehensive. Though it's a little redundant, I think it makes sense. What do you think?

[freakboy3742]

Almost there! A couple more revisions; also - if we're adding a whole section about configurating color (which I agree is a good idea), we can remove the reference to the splash background on L100-101.

[freakboy3742]

There's no need to list all the things that can be configured just before you list all the things that can be configured :-)

Suggested change

	In addition to ``splash_background_color``, Android projects allow for
	configuration of an ``accent_color``, ``primary_color``, and
	``primary_color_dark``.
	Android allows for some customization of the colors used by your app:

[bbusenius]

Fair point! :-)

[freakboy3742]

Suggested change

	* ``accent_color`` is used subtly throughout an Android app to call attention
	to key elements. It's used on things like form labels and inputs.
	* ``accent_color`` is used as a subtle highlight throughout your app to call attention
	to key elements. It's used on things like form labels and inputs.

[bbusenius]

I made all those changes. Thanks for helping me get this in shape!

[freakboy3742]

Awesome! Thanks for the patch, and for persisting through all the nitpicking edits!