RFR: 8321573: Enhance documentation for Platform.Preferences.accentColor

[Michael Strauß]

This PR enhances the documentation of `Platform.Preferences.accentColor`:


   /**
-   * The accent color.
+   * The accent color, which is usually a vivid color that contrasts with the foreground
+   * and background colors. It can be used to highlight the active or important part of a
+   * control and make it stand out from the rest of the user interface.

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Commit messages:
 - added accent color documentation

Changes: https://git.openjdk.org/jfx/pull/1301/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1301&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321573
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1301.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1301/head:pull/1301

PR: https://git.openjdk.org/jfx/pull/1301