diff --git a/gui/main.qml b/gui/main.qml
index 7d24c2e..abf3ed6 100644
--- a/gui/main.qml
+++ b/gui/main.qml
@@ -282,15 +282,33 @@ ApplicationWindow {
                             height: 22
                             radius: 3
                             color: {
-                                switch (blockType) {
-                                case "user":      return Qt.lighter(theme.highlightColor, 1.8)
-                                case "assistant": return Qt.lighter(theme.linkColor, 1.8)
-                                case "reasoning": return Qt.lighter(theme.midColor, 1.5)
-                                case "call":      return Qt.lighter(theme.buttonColor, 1.1)
-                                case "tool":      return Qt.lighter(theme.darkColor, 2.0)
-                                case "error":     return Qt.lighter("#e53935", 1.6)
-                                case "info":      return Qt.lighter(theme.midColor, 1.3)
-                                default:          return theme.baseColor
+                                // Derive header colors from base background with subtle tint.
+                                // Always readable because text uses theme.textColor.
+                                var bg = theme.baseColor
+                                if (theme.isDark) {
+                                    // Dark theme: lighter tints against dark background
+                                    switch (blockType) {
+                                    case "user":      return Qt.lighter(bg, 1.8)
+                                    case "assistant": return Qt.lighter(bg, 1.5)
+                                    case "reasoning": return Qt.lighter(bg, 1.3)
+                                    case "call":      return Qt.lighter(bg, 1.7)
+                                    case "tool":      return Qt.lighter(bg, 1.2)
+                                    case "error":     return Qt.rgba(0.6, 0.15, 0.15, 0.7)
+                                    case "info":      return Qt.lighter(bg, 1.4)
+                                    default:          return bg
+                                    }
+                                } else {
+                                    // Light theme: slightly darker tints
+                                    switch (blockType) {
+                                    case "user":      return Qt.darker(bg, 1.12)
+                                    case "assistant": return Qt.darker(bg, 1.06)
+                                    case "reasoning": return Qt.darker(bg, 1.03)
+                                    case "call":      return Qt.darker(bg, 1.1)
+                                    case "tool":      return Qt.darker(bg, 1.04)
+                                    case "error":     return Qt.rgba(1.0, 0.8, 0.8, 0.7)
+                                    case "info":      return Qt.darker(bg, 1.02)
+                                    default:          return bg
+                                    }
                                 }
                             }