refactor: use __fish_palette in small utility functions (2/2)

25 duplicated declarations replaced by 7 calls. Completes the 33 structural
conversions: 167 declarations removed, 33 calls added, and --structural
confirms every one of the 33 diffs is declaration removals plus inserted
calls only -- no rendering text touched.

functions/y.fish is the one file in the repo with no trailing newline on
main; its original file ending is preserved rather than normalised.

functions/spark.fish

@@ -29,11 +29,7 @@ function spark --description 'Sparklines'
     if set --query _flag_version[1]
         echo "spark, version 1.1.0"
     else if set --query _flag_help[1]
-        set -l c_head (set_color --bold cyan)
-        set -l c_cmd (set_color --bold)
-        set -l c_flag (set_color yellow)
-        set -l c_arg (set_color cyan)
-        set -l c_reset (set_color normal)
+        __fish_palette
         echo "$c_head""Usage:$c_reset $c_cmd""spark$c_reset $c_arg""<numbers ...>$c_reset"
         echo "       stdin | $c_cmd""spark$c_reset"
         echo "$c_head""Options:$c_reset"