Fix the brighten() channel swap and use semantic colours for placeholders

Vault/Sources/VaultFeed/Models/VaultItemColor.swift

@@ -57,8 +57,8 @@ extension VaultItemColor {
         // Standard brightness components for each channel, based on the human eye.
         VaultItemColor(
             red: (red + amount * 0.299).clamped(to: 0 ... 1),
-            green: (blue + amount * 0.114).clamped(to: 0 ... 1),
-            blue: (green + amount * 0.587).clamped(to: 0 ... 1),
+            green: (green + amount * 0.587).clamped(to: 0 ... 1),
+            blue: (blue + amount * 0.114).clamped(to: 0 ... 1),
         )
     }
 }

Vault/Sources/VaultiOS/Views/Previews/OTP/HOTPCodePreviewView.swift

@@ -49,14 +49,14 @@ struct HOTPCodePreviewView<ButtonView: View>: View {
         case .normal:
             switch previewViewModel.code {
             case .visible, .locked:
-                Color.blue
+                Color.accentColor
             case .notReady, .obfuscated:
-                Color.gray
+                Color(.quaternarySystemFill)
             case .error, .finished:
                 Color.red
             }
         case .editingState:
-            Color.blue
+            Color.accentColor
         }
     }
 

Vault/Sources/VaultiOS/Views/Previews/OTP/TOTPCodePreviewView.swift

@@ -106,7 +106,7 @@ struct TOTPCodePreviewView<TimerBar: View>: View {
             case .visible, .locked:
                 timerView
             case .finished, .notReady, .obfuscated:
-                Color.gray
+                Color(.quaternarySystemFill)
                     .redacted(reason: .placeholder)
             case .error:
                 Color.red

Vault/Sources/VaultiOSWidgets/Views/OTPWidgetAccessoryRectangularView.swift

@@ -39,7 +39,7 @@ struct OTPWidgetAccessoryRectangularView: View {
             )
             .progressViewStyle(.linear)
         case .hotp, .unavailable, .placeholder:
-            Color.gray.opacity(0.3).clipShape(Capsule())
+            Color(.quaternarySystemFill).clipShape(Capsule())
         }
     }
 

Vault/Sources/VaultiOSWidgets/Views/OTPWidgetSmallView.swift

@@ -77,7 +77,7 @@ struct OTPWidgetSmallView: View {
             .progressViewStyle(.linear)
             .tint(.accentColor)
         case .hotp, .unavailable, .placeholder:
-            Color.gray.opacity(0.3)
+            Color(.quaternarySystemFill)
         }
     }
 

Vault/Tests/VaultFeedTests/Models/VaultItemColorTests.swift

@@ -0,0 +1,59 @@
+import Foundation
+import Testing
+@testable import VaultFeed
+
+struct VaultItemColorTests {
+    @Test
+    func brighten_appliesEachChannelsOwnLuminanceWeight() {
+        let color = VaultItemColor(red: 0.1, green: 0.2, blue: 0.3)
+
+        let result = color.brighten(amount: 1)
+
+        // Each channel is offset by its own coefficient, not another channel's.
+        #expect(abs(result.red - (0.1 + 0.299)) < 0.0001)
+        #expect(abs(result.green - (0.2 + 0.587)) < 0.0001)
+        #expect(abs(result.blue - (0.3 + 0.114)) < 0.0001)
+    }
+
+    /// Regression cover for a channel swap: `green` was derived from `blue` and `blue` from
+    /// `green`, so brightening rotated the hue instead of lightening it.
+    @Test
+    func brighten_doesNotSwapGreenAndBlue() {
+        let color = VaultItemColor(red: 0, green: 1, blue: 0)
+
+        let result = color.brighten(amount: 0)
+
+        #expect(result == color)
+    }
+
+    @Test
+    func brighten_isMonotonicPerChannel() {
+        let color = VaultItemColor(red: 0.4, green: 0.4, blue: 0.4)
+
+        let brighter = color.brighten(amount: 0.5)
+        let darker = color.brighten(amount: -0.5)
+
+        #expect(brighter.red > color.red)
+        #expect(brighter.green > color.green)
+        #expect(brighter.blue > color.blue)
+        #expect(darker.red < color.red)
+        #expect(darker.green < color.green)
+        #expect(darker.blue < color.blue)
+    }
+
+    @Test
+    func brighten_clampsToUnitRange() {
+        let light = VaultItemColor(red: 0.95, green: 0.95, blue: 0.95)
+        let dark = VaultItemColor(red: 0.05, green: 0.05, blue: 0.05)
+
+        let overBright = light.brighten(amount: 5)
+        let overDark = dark.brighten(amount: -5)
+
+        #expect(overBright.red == 1)
+        #expect(overBright.green == 1)
+        #expect(overBright.blue == 1)
+        #expect(overDark.red == 0)
+        #expect(overDark.green == 0)
+        #expect(overDark.blue == 0)
+    }
+}

VaultApp/VaultWidgets/Assets.xcassets/AccentColor.colorset/Contents.json

@@ -1,6 +1,10 @@
 {
   "colors" : [
     {
+      "color" : {
+        "platform" : "universal",
+        "reference" : "systemBlueColor"
+      },
       "idiom" : "universal"
     }
   ],