You can now see which traits are unread and mark them read by clicking

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/trait/TraitDiscovery.java

@@ -11,6 +11,7 @@ import org.jetbrains.annotations.Nullable;
 
 import com.minelittlepony.unicopia.entity.player.Pony;
 import com.minelittlepony.unicopia.network.Channel;
+import com.minelittlepony.unicopia.network.MsgMarkTraitRead;
 import com.minelittlepony.unicopia.network.MsgUnlockTraits;
 import com.minelittlepony.unicopia.util.NbtSerialisable;
 
@@ -48,10 +49,16 @@ public class TraitDiscovery implements NbtSerialisable {
         pony.setDirty();
     }
 
-    public void markRead() {
+    @Environment(EnvType.CLIENT)
-        unreadTraits.clear();
+    public void markRead(Trait trait) {
+        Channel.MARK_TRAIT_READ.send(new MsgMarkTraitRead(Set.of(trait)));
+    }
+
+    public void markRead(Set<Trait> traits) {
+        if (unreadTraits.removeAll(traits)) {
             pony.setDirty();
         }
+    }
 
     public void unlock(Item item) {
         if (item == Items.AIR) {

src/main/java/com/minelittlepony/unicopia/container/SpellbookScreen.java

@@ -238,6 +238,8 @@ public class SpellbookScreen extends HandledScreen<SpellbookScreenHandler> {
                     .append("\n")
                     .append(new TranslatableText("gui.unicopia.trait.corruption", ItemStack.MODIFIER_FORMAT.format(trait.getGroup().getCorruption())).formatted(Formatting.ITALIC, corruptionColor)))
                     , 200));
+
+            onClick(sender -> Pony.of(client.player).getDiscoveries().markRead(trait));
         }
 
         @Override
@@ -249,7 +251,14 @@ public class SpellbookScreen extends HandledScreen<SpellbookScreenHandler> {
             RenderSystem.setShaderTexture(0, TEXTURE);
             RenderSystem.enableBlend();
             drawTexture(matrices, x - 2, y - 8, 204, 219, 22, 32, 512, 256);
+
+            if (!active) {
                 drawTexture(matrices, x - 2, y - 1, 74, 223, 18, 18, 512, 256);
+            }
+
+            if (discoveries.isUnread(trait)) {
+                drawTexture(matrices, x - 8, y - 8, 225, 219, 35, 32, 512, 256);
+            }
 
             super.renderButton(matrices, mouseX, mouseY, partialTicks);
             hovered &= active;

src/main/java/com/minelittlepony/unicopia/network/Channel.java

@@ -12,6 +12,7 @@ import net.minecraft.util.Identifier;
 public interface Channel {
     C2SPacketType<MsgPlayerAbility<?>> CLIENT_PLAYER_ABILITY = SimpleNetworking.clientToServer(new Identifier("unicopia", "player_ability"), MsgPlayerAbility::new);
     C2SPacketType<MsgRequestSpeciesChange> CLIENT_REQUEST_SPECIES_CHANGE = SimpleNetworking.clientToServer(new Identifier("unicopia", "request_capabilities"), MsgRequestSpeciesChange::new);
+    C2SPacketType<MsgMarkTraitRead> MARK_TRAIT_READ = SimpleNetworking.clientToServer(new Identifier("unicopia", "mark_trait_read"), MsgMarkTraitRead::new);
 
     S2CPacketType<MsgPlayerCapabilities> SERVER_PLAYER_CAPABILITIES = SimpleNetworking.serverToClient(new Identifier("unicopia", "player_capabilities"), MsgPlayerCapabilities::new);
     S2CPacketType<MsgSpawnProjectile> SERVER_SPAWN_PROJECTILE = SimpleNetworking.serverToClient(new Identifier("unicopia", "projectile_entity"), MsgSpawnProjectile::new);

src/main/java/com/minelittlepony/unicopia/network/MsgMarkTraitRead.java

@@ -0,0 +1,38 @@
+package com.minelittlepony.unicopia.network;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import com.minelittlepony.unicopia.ability.magic.spell.trait.Trait;
+import com.minelittlepony.unicopia.entity.player.Pony;
+import com.minelittlepony.unicopia.util.network.Packet;
+
+import net.minecraft.network.PacketByteBuf;
+import net.minecraft.server.network.ServerPlayerEntity;
+
+public class MsgMarkTraitRead implements Packet<ServerPlayerEntity> {
+
+    public final Set<Trait> traits = new HashSet<>();
+
+    MsgMarkTraitRead(PacketByteBuf buffer) {
+        int length = buffer.readInt();
+        for (int i = 0; i < length; i++) {
+            Trait.fromId(buffer.readIdentifier()).ifPresent(traits::add);
+        }
+    }
+
+    public MsgMarkTraitRead(Set<Trait> traits) {
+        this.traits.addAll(traits);
+    }
+
+    @Override
+    public void toBuffer(PacketByteBuf buffer) {
+        buffer.writeInt(traits.size());
+        traits.forEach(trait -> buffer.writeIdentifier(trait.getId()));
+    }
+
+    @Override
+    public void handle(ServerPlayerEntity sender) {
+        Pony.of(sender).getDiscoveries().markRead(traits);
+    }
+}