diff --git a/build.sbt b/build.sbt
index cfdb483e2..c0c11847d 100644
--- a/build.sbt
+++ b/build.sbt
@@ -38,7 +38,7 @@ lazy val scalachess = Project("scalachess", file(".")).settings(
 )
 
 ThisBuild / organization      := "org.lichess"
-ThisBuild / version           := "15.3.5"
+ThisBuild / version           := "15.3.6"
 ThisBuild / scalaVersion      := "3.3.0"
 ThisBuild / licenses += "MIT" -> url("https://opensource.org/licenses/MIT")
 
diff --git a/src/main/scala/ByColor.scala b/src/main/scala/ByColor.scala
index d7dc9c3f3..947affa6a 100644
--- a/src/main/scala/ByColor.scala
+++ b/src/main/scala/ByColor.scala
@@ -1,8 +1,9 @@
 package chess
 
-import cats.{ Applicative, Eq }
+import cats.{ Applicative, Eq, Functor, Monoid }
 import cats.syntax.all.*
 import scala.annotation.targetName
+import alleycats.Zero
 
 case class ByColor[A](white: A, black: A):
 
@@ -78,9 +79,24 @@ case class ByColor[A](white: A, black: A):
 object ByColor:
   def apply[A](a: A): ByColor[A]          = ByColor(a, a)
   def apply[A](f: Color => A): ByColor[A] = ByColor(white = f(White), black = f(Black))
+  def apply[F[_], A](f: Color => F[A]): Applicative[F] ?=> F[ByColor[A]] =
+    (f(White), f(Black)).mapN(ByColor(_, _))
 
   given [A: Eq]: Eq[ByColor[A]] with
     def eqv(x: ByColor[A], y: ByColor[A]) =
       x.white === y.white && x.black === y.black
 
+  given [A: Zero]: Zero[ByColor[A]] with
+    def zero = ByColor(Zero[A].zero)
+
+  given [A: Monoid]: Monoid[ByColor[A]] with
+    def empty = ByColor(Monoid[A].empty)
+    def combine(x: ByColor[A], y: ByColor[A]) =
+      ByColor(Monoid[A].combine(x.white, y.white), Monoid[A].combine(x.black, y.black))
+
+  given Functor[ByColor] with
+    def map[A, B](fa: ByColor[A])(f: A => B): ByColor[B] = fa.map(f)
+
   extension [A](bc: ByColor[IterableOnce[A]]) def flatten: List[A] = bc.all.flatten
+
+  extension [A](p: (A, A)) def asByColor: ByColor[A] = ByColor(p._1, p._2)
diff --git a/src/main/scala/Hash.scala b/src/main/scala/Hash.scala
index 3cf073794..e73019282 100644
--- a/src/main/scala/Hash.scala
+++ b/src/main/scala/Hash.scala
@@ -104,7 +104,7 @@ object Hash extends OpaqueInt[Hash]:
       data.pockets
         .mapWithColor: (color, pocket) =>
           val colorshift = color.fold(79, -1)
-          pocket.map((role, size) => crazyPocketMask(role, colorshift, size))
+          pocket.flatMap((role, size) => crazyPocketMask(role, colorshift, size))
         .flatten
         .computeHash(hcrazypromotions)
 
diff --git a/src/main/scala/Role.scala b/src/main/scala/Role.scala
index 37d7fb578..0f96ee3c9 100644
--- a/src/main/scala/Role.scala
+++ b/src/main/scala/Role.scala
@@ -9,6 +9,8 @@ sealed trait Role:
   lazy val forsythUpper: Char = forsyth.toUpper
   lazy val pgn: Char          = forsythUpper
   lazy val name               = toString.toLowerCase
+  inline def forsythBy(color: Color): Char =
+    if color.white then forsythUpper else forsyth
 
 sealed trait PromotableRole extends Role
 
diff --git a/src/main/scala/variant/Crazyhouse.scala b/src/main/scala/variant/Crazyhouse.scala
index 196a3e7eb..71240ee91 100644
--- a/src/main/scala/variant/Crazyhouse.scala
+++ b/src/main/scala/variant/Crazyhouse.scala
@@ -175,7 +175,7 @@ case object Crazyhouse
     def store(piece: Piece): Pockets =
       pockets.update(!piece.color, _.store(piece.role))
 
-    def forsyth = pockets.white.forsythUpper + pockets.black.forsyth
+    def forsyth = pockets.reduce(_.forsythUpper + _.forsyth)
 
   case class Pocket(pawn: Int, knight: Int, bishop: Int, rook: Int, queen: Int):
 
@@ -228,9 +228,12 @@ case object Crazyhouse
       case Queen  => f(queen).map(x => copy(queen = x))
       case King   => None
 
-    def map[B](f: (Role, Int) => Option[B]): List[B] =
+    def flatMap[B](f: (Role, Int) => IterableOnce[B]): List[B] =
       List(f(Pawn, pawn), f(Knight, knight), f(Bishop, bishop), f(Rook, rook), f(Queen, queen)).flatten
 
+    def map[B](f: (Role, Int) => B): List[B] =
+      List(f(Pawn, pawn), f(Knight, knight), f(Bishop, bishop), f(Rook, rook), f(Queen, queen))
+
   object Pocket:
     val empty = Pocket(0, 0, 0, 0, 0)
     def apply(roles: List[Role]): Pocket =