diff --git a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/data/action/ContentMode.kt b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/data/action/ContentMode.kt
new file mode 100644
index 0000000..52f11d9
--- /dev/null
+++ b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/data/action/ContentMode.kt
@@ -0,0 +1,40 @@
+package cn.rdlevel.rdkt.core.data.action
+
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+/**
+ * Represents how the content will be rescaled in [SetBackgroundColorEvent][cn.rdlevel.rdkt.core.events.SetBackgroundColorEvent].
+ */
+@Serializable
+public enum class ContentMode {
+    /**
+     * Rescale the content to fill the space.
+     */
+    @SerialName("ScaleToFill")
+    SCALE_TO_FILL,
+
+    /**
+     * Rescale the content to fit the space while maintaining its aspect ratio.
+     */
+    @SerialName("AspectFit")
+    ASPECT_FIT,
+
+    /**
+     * Rescale the content to fill the space while maintaining its aspect ratio.
+     */
+    @SerialName("AspectFill")
+    ASPECT_FILL,
+
+    /**
+     * Center the content in the space.
+     */
+    @SerialName("Center")
+    CENTER,
+
+    /**
+     * Tile the content in the space.
+     */
+    @SerialName("Tiled")
+    TILED,
+}
\ No newline at end of file
diff --git a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/data/action/RescaleFilter.kt b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/data/action/RescaleFilter.kt
new file mode 100644
index 0000000..98f30a3
--- /dev/null
+++ b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/data/action/RescaleFilter.kt
@@ -0,0 +1,22 @@
+package cn.rdlevel.rdkt.core.data.action
+
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+/**
+ * Represent how to render the image when the image is rescaled.
+ */
+@Serializable
+public enum class RescaleFilter {
+    /**
+     * The color of the rescaled pixel will be the nearest neighbor's.
+     */
+    @SerialName("NearestNeighbor")
+    NEAREST_NEIGHBOR,
+
+    /**
+     * The color of the rescaled pixel will be a weighted average of the nearest neighbors.
+     */
+    @SerialName("Bilinear")
+    BILINEAR,
+}
\ No newline at end of file
diff --git a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/data/action/TilingConfig.kt b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/data/action/TilingConfig.kt
new file mode 100644
index 0000000..5a80e41
--- /dev/null
+++ b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/data/action/TilingConfig.kt
@@ -0,0 +1,36 @@
+package cn.rdlevel.rdkt.core.data.action
+
+import cn.rdlevel.rdkt.core.data.Easing
+import cn.rdlevel.rdkt.core.data.Vector2
+import cn.rdlevel.rdkt.core.data.vectorOf
+import kotlinx.serialization.Serializable
+
+/**
+ * Represents how the content should be tiled.
+ *
+ * @property tilingType The type of tiling to apply.
+ * @property scrollX The X component of the scroll speed of the tiling in px.
+ * @property scrollY The Y component of the scroll speed of the tiling in px.
+ * @property duration The duration of the tiling animation change in beats.
+ * @property interval The interval between pulses in beats when [tilingType] is [TilingType.PULSE].
+ * @property ease The easing function for the tiling animation change.
+ */
+@Serializable
+public data class TilingConfig(
+    var tilingType: TilingType = TilingType.SCROLL,
+    var scrollX: Double = 0.0,
+    var scrollY: Double = 0.0,
+    var duration: Double = 0.0,
+    var interval: Double = 1.0,
+    var ease: Easing = Easing.LINEAR,
+) {
+    /**
+     * The scroll speed of the tiling in px.
+     */
+    var scroll: Vector2
+        get() = vectorOf(scrollX, scrollY)
+        set(value) {
+            scrollX = value.x
+            scrollY = value.y
+        }
+}
\ No newline at end of file
diff --git a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/data/action/TilingType.kt b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/data/action/TilingType.kt
new file mode 100644
index 0000000..b1be596
--- /dev/null
+++ b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/data/action/TilingType.kt
@@ -0,0 +1,22 @@
+package cn.rdlevel.rdkt.core.data.action
+
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+/**
+ * Represents the tiling type of tiled content.
+ */
+@Serializable
+public enum class TilingType {
+    /**
+     * The content will be scrolling.
+     */
+    @SerialName("Scroll")
+    SCROLL,
+
+    /**
+     * The content will be pulsing repeatedly.
+     */
+    @SerialName("Pulse")
+    PULSE,
+}
\ No newline at end of file
diff --git a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetBackgroundColorEvent.kt b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetBackgroundColorEvent.kt
new file mode 100644
index 0000000..3508812
--- /dev/null
+++ b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetBackgroundColorEvent.kt
@@ -0,0 +1,74 @@
+@file:OptIn(RDKTInternalAPI::class, ExperimentalSerializationApi::class)
+
+package cn.rdlevel.rdkt.core.events
+
+
+import cn.rdlevel.rdkt.core.annotations.RDKTInternalAPI
+import cn.rdlevel.rdkt.core.data.*
+import cn.rdlevel.rdkt.core.data.action.ContentMode
+import cn.rdlevel.rdkt.core.data.action.RescaleFilter
+import cn.rdlevel.rdkt.core.data.action.TilingConfig
+import cn.rdlevel.rdkt.core.serialization.Flatten
+import cn.rdlevel.rdkt.core.serialization.flatten
+import kotlinx.serialization.*
+import kotlinx.serialization.json.JsonClassDiscriminator
+
+/**
+ * Sets the background of rooms.
+ * @property type The type of the background.
+ * @property filter How should the pixels' color of the background be when rescaled.
+ */
+@ConsistentCopyVisibility
+@Serializable(SetBackgroundColorEvent.Serializer::class)
+@KeepGeneratedSerializer
+@SerialName("SetBackgroundColor")
+public data class SetBackgroundColorEvent private constructor(
+    @Flatten
+    private var type: Type,
+    var filter: RescaleFilter = RescaleFilter.NEAREST_NEIGHBOR,
+    override val rooms: RoomsOrTopLayer = roomsOf(ROOM1),
+) : ActionEvent(), RoomsOrTopLayerSpecificEvent {
+    /**
+     * Represents the type and the settings of the background.
+     */
+    @Serializable
+    @JsonClassDiscriminator("backgroundType")
+    public sealed class Type {
+        /**
+         * The color of the background.
+         */
+        public abstract var color: ColorWithAlpha
+
+        /**
+         * Represents a pure color background.
+         */
+        @SerialName("Color")
+        @Serializable
+        public data class Color(override var color: ColorWithAlpha = WHITE) : Type()
+
+        /**
+         * Represents a background with images.
+         *
+         * @property image The images to be used. When there's none, it clears the image background. When there are multiple, they will be played in a loop.
+         * @property color The color filter to be applied on images.
+         * @property fps The speed of the image loop in frames per second when there are multiple images.
+         * @property contentMode The content mode of the images.
+         * @property tilingConfig The tiling configuration of the images when [contentMode] is [ContentMode.TILED].
+         */
+        @SerialName("Image")
+        @Serializable(Image.Serializer::class)
+        @KeepGeneratedSerializer
+        public data class Image(
+            var image: List<String> = listOf(),
+            override var color: ColorWithAlpha = WHITE,
+            var fps: Double = 30.0,
+            var contentMode: ContentMode = ContentMode.SCALE_TO_FILL,
+            @Flatten
+            var tilingConfig: TilingConfig = TilingConfig()
+        ) : Type() {
+            public object Serializer : KSerializer<Image> by generatedSerializer().flatten()
+        }
+    }
+
+    public object Serializer : KSerializer<SetBackgroundColorEvent> by generatedSerializer().flatten()
+}
\ No newline at end of file