[9.0] [ColorMapping] Fix palette key mapping for legacy palette ids (#…

…211858) (#211920)

# Backport

This will backport the following commits from `main` to `9.0`:
- [[ColorMapping] Fix palette key mapping for legacy palette ids
(#211858)](#211858)

<!--- Backport version: 9.6.6 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sorenlouv/backport)

<!--BACKPORT [{"author":{"name":"Nick
Partridge","email":"nicholas.partridge@elastic.co"},"sourceCommit":{"committedDate":"2025-02-20T15:31:55Z","message":"[ColorMapping]
Fix palette key mapping for legacy palette ids (#211858)\n\nCurrently,
palettes with the legacy palette id of `eui_amsterdam_color_blind`, the
old default id, gets assigned the `kibana 7` palette. The desired
behavior is that this palette is assigned the new borealis default
palette in
`9.0`.","sha":"9e7d93189f6ea59fb21332fd7e0af571a4bac8c0","branchLabelMapping":{"^v9.1.0$":"main","^v8.19.0$":"8.x","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["Team:Visualizations","release_note:skip","Feature:Lens","v9.0.0","backport:version","v9.1.0"],"title":"[ColorMapping]
Fix palette key mapping for legacy palette
ids","number":211858,"url":"https://github.com/elastic/kibana/pull/211858","mergeCommit":{"message":"[ColorMapping]
Fix palette key mapping for legacy palette ids (#211858)\n\nCurrently,
palettes with the legacy palette id of `eui_amsterdam_color_blind`, the
old default id, gets assigned the `kibana 7` palette. The desired
behavior is that this palette is assigned the new borealis default
palette in
`9.0`.","sha":"9e7d93189f6ea59fb21332fd7e0af571a4bac8c0"}},"sourceBranch":"main","suggestedTargetBranches":["9.0"],"targetPullRequestStates":[{"branch":"9.0","label":"v9.0.0","branchLabelMappingKey":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"},{"branch":"main","label":"v9.1.0","branchLabelMappingKey":"^v9.1.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/211858","number":211858,"mergeCommit":{"message":"[ColorMapping]
Fix palette key mapping for legacy palette ids (#211858)\n\nCurrently,
palettes with the legacy palette id of `eui_amsterdam_color_blind`, the
old default id, gets assigned the `kibana 7` palette. The desired
behavior is that this palette is assigned the new borealis default
palette in `9.0`.","sha":"9e7d93189f6ea59fb21332fd7e0af571a4bac8c0"}}]}]
BACKPORT-->

Co-authored-by: Nick Partridge <nicholas.partridge@elastic.co>

src/platform/packages/shared/kbn-palettes/classes/palettes.ts

@@ -37,7 +37,7 @@ export class KbnPalettes {
 function buildAliasMappings(palettes: IKbnPalette[]): Map<string, string> {
   return palettes.reduce((acc, { id, aliases }) => {
     aliases.forEach((alias) => {
-      acc.set(alias, id);
+      if (!acc.has(alias)) acc.set(alias, id);
     });
     return acc;
   }, new Map());

src/platform/packages/shared/kbn-palettes/palettes/categorical/elastic.ts

@@ -20,6 +20,7 @@ export const elasticPalette = new KbnColorFnPalette({
   id: KbnPalette.Default,
   type: 'categorical',
   aliases: [
+    KbnPalette.Default, // needed when switching between new and old themes
     'elastic_borealis', // placeholder - not yet used
     KbnPalette.Amsterdam, // to assign to existing default palettes
   ],