Refactor hardcoded color to use OUI in region_map (#4299)

* Refactor hardcoded color to use OUI

Signed-off-by: Matt Provost <provomat@amazon.com>

* Update changelog

Signed-off-by: Matt Provost <provomat@amazon.com>

---------

Signed-off-by: Matt Provost <provomat@amazon.com>
Signed-off-by: Josh Romero <rmerqg@amazon.com>
Co-authored-by: Josh Romero <rmerqg@amazon.com>

CHANGELOG.md

@@ -73,6 +73,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Replace the use of `bluebird` in `saved_objects` plugin ([#4026](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/4026))
 - Relocate tutorials imagery into `src/plugins/home/public/assets/tutorials/logos` ([#4382](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/4382))
 - [VisBuilder] Use OUI icon ([#4446](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/4446))
+- [Vis Colors] [Region Maps] Replace hardcode color to OUI color in `region_map` plugin ([#4299](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/4299))
 - [Vis Colors] Replace color maps with OUI color palettes ([#4293](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/4293))
 - [Vis Colors] [Maps] Replace hardcoded color to OUI color in `maps_legacy` plugin ([#4294](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/4294))
 - [Vis Colors] [TSVB] Update default color in `vis_type_timeseries` to use `ouiPaletteColorBlind()[0]`([#4363](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/4363))

src/plugins/region_map/public/choropleth_layer.js

@@ -32,6 +32,7 @@ import $ from 'jquery';
 import _ from 'lodash';
 import d3 from 'd3';
 import { i18n } from '@osd/i18n';
+import { euiThemeVars } from '@osd/ui-shared-deps/theme';
 import * as topojson from 'topojson-client';
 import { getNotifications } from './opensearch_dashboards_services';
 import { colorUtil, OpenSearchDashboardsMapLayer } from '../../maps_legacy/public';
@@ -46,7 +47,7 @@ import {
 const EMPTY_STYLE = {
   weight: 1,
   opacity: 0.6,
-  color: 'rgb(200,200,200)',
+  color: euiThemeVars.euiColorMediumShade,
   fillOpacity: 0,
 };