diff --git a/BusinessCard/Models/CardTheme.swift b/BusinessCard/Models/CardTheme.swift
index 068f21e..65c775d 100644
--- a/BusinessCard/Models/CardTheme.swift
+++ b/BusinessCard/Models/CardTheme.swift
@@ -121,12 +121,26 @@ struct CardTheme: Identifiable, Hashable, Sendable {
     
     private var secondaryRGB: (Double, Double, Double) {
         if let rgb = customRGB {
-            // Create a lighter/darker variant for gradient
-            return (
-                min(1.0, rgb.0 + 0.2),
-                min(1.0, rgb.1 + 0.15),
-                min(1.0, rgb.2 + 0.1)
-            )
+            // Calculate luminance to determine if we should lighten or darken
+            let luminance = 0.299 * rgb.0 + 0.587 * rgb.1 + 0.114 * rgb.2
+            
+            if luminance < 0.3 {
+                // Dark color: lighten uniformly to avoid color shifts
+                let lightenAmount = 0.15
+                return (
+                    min(1.0, rgb.0 + lightenAmount),
+                    min(1.0, rgb.1 + lightenAmount),
+                    min(1.0, rgb.2 + lightenAmount)
+                )
+            } else {
+                // Light color: darken uniformly
+                let darkenAmount = 0.12
+                return (
+                    max(0.0, rgb.0 - darkenAmount),
+                    max(0.0, rgb.1 - darkenAmount),
+                    max(0.0, rgb.2 - darkenAmount)
+                )
+            }
         }
         guard let preset else { return (0.93, 0.83, 0.68) }
         switch preset {