RFR: 8324327: ColorPicker shows a white rectangle on clicking on picker

[Andy Goryachev]

Root cause: premature 'return' from initialization code leaves the hover square visible, even when it should be hidden, as the case is when the color value is not present in the palette.

- added unit tests

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Commit messages:
 - 8324327: ColorPicker shows a white rectangle on clicking on picker

Changes: https://git.openjdk.org/jfx/pull/1458/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1458&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324327
  Stats: 64 lines in 2 files changed: 52 ins; 6 del; 6 mod
  Patch: https://git.openjdk.org/jfx/pull/1458.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1458/head:pull/1458

PR: https://git.openjdk.org/jfx/pull/1458