Fix T83988: Active modifier outline uses search theme color

The outline for the active modifier was abusing the property search
match theme color, as noted in a comment. This commit adds a new
theme color in RNA specifically for the active modifier outline.

release/datafiles/userdef/userdef_default_theme.c

@@ -287,6 +287,7 @@ const bTheme U_theme_default = {
     .outline_width = 1,
     .facedot_size = 4,
     .match = RGBA(0x5680c2ff),
+    .active = RGBA(0x5680c2ff),
   },
   .space_view3d = {
     .back = RGBA(0x393939ff),

release/scripts/presets/interface_theme/blender_light.xml

@@ -855,6 +855,7 @@
     <properties>
       <ThemeProperties
         match="#5680c2"
+        active_modifier="#5680c2ff"
         >
         <space>
           <ThemeSpaceGeneric

source/blender/blenloader/intern/versioning_userdef.c

@@ -272,6 +272,7 @@ static void do_versions_theme(const UserDef *userdef, bTheme *btheme)
    */
   {
     /* Keep this block, even when empty. */
+    FROM_DEFAULT_V4_UCHAR(space_properties.active);
   }
 
 #undef FROM_DEFAULT_V4_UCHAR

source/blender/editors/interface/interface_panel.c

@@ -1119,16 +1119,15 @@ static void panel_draw_highlight_border(const Panel *panel,
     radius = 0.0f;
   }
 
-  /* Abuse the property search theme color for now. */
   float color[4];
-  UI_GetThemeColor4fv(TH_MATCH, color);
-  UI_draw_roundbox_aa(false,
-                      rect->xmin,
-                      UI_panel_is_closed(panel) ? header_rect->ymin : rect->ymin,
-                      rect->xmax,
-                      header_rect->ymax,
-                      radius,
-                      color);
+  UI_GetThemeColor4fv(TH_SELECT_ACTIVE, color);
+  UI_draw_roundbox_4fv(false,
+                       rect->xmin,
+                       UI_panel_is_closed(panel) ? header_rect->ymin : rect->ymin,
+                       rect->xmax,
+                       header_rect->ymax,
+                       radius,
+                       color);
 }
 
 static void panel_draw_aligned_widgets(const uiStyle *style,

source/blender/makesrna/intern/rna_userdef.c

@@ -3005,6 +3005,12 @@ static void rna_def_userdef_theme_space_buts(BlenderRNA *brna)
   RNA_def_property_ui_text(prop, "Search Match", "");
   RNA_def_property_update(prop, 0, "rna_userdef_theme_update");
 
+  prop = RNA_def_property(srna, "active_modifier", PROP_FLOAT, PROP_COLOR_GAMMA);
+  RNA_def_property_float_sdna(prop, NULL, "active");
+  RNA_def_property_array(prop, 4);
+  RNA_def_property_ui_text(prop, "Active Modifier Outline", "");
+  RNA_def_property_update(prop, 0, "rna_userdef_theme_update");
+
   rna_def_userdef_theme_spaces_main(srna);
 }