Better grouping for alt style series names in the filter dropdown

app/assets/stylesheets/alt_styles/index.sass

@@ -1,3 +1,13 @@
+@import "../partials/clean/constants"
+
+// Prefer to break the name at certain points.
 .rainbow-pool-list
 	.name span
 		display: inline-block
+
+// De-emphasize Prismatic styles, in browsers that support it.
+.rainbow-pool-filters
+	select[name="series"]
+		option[value*=": "]
+			color: $soft-text-color
+			font-style: italic

app/models/alt_style.rb

@@ -106,7 +106,9 @@ class AltStyle < ApplicationRecord
   end
 
   def self.all_series_names
-    distinct.where.not(series_name: nil).pluck(:series_name).sort
+    # Sort by the part *after* the colon, then before (if any).
+    distinct.where.not(series_name: nil).pluck(:series_name).
+      sort_by { |series_name| series_name.split(': ', 2).reverse }
   end
 
   def self.all_supported_colors