fix: xterm-256 cube uses 0xd7 not 0xdf for level-4 color (palette typo)

src/main/java/li/cil/oc2/common/vm/terminal/color/TerminalColors.java

@@ -3,22 +3,22 @@
 import com.google.gson.annotations.SerializedName;
 
 public final class TerminalColors {
     public static final int[] BRIGHT_COLORS = {
         0x555555, 0xFF5555, 0x55FF55, 0xFFFF55,
         0x5555FF, 0xFF55FF, 0x55FFFF, 0xFFFFFF,
     };
 
     public static final int[] COLORS = {
         0x000000, 0xAA0000, 0x00AA00, 0xAAAA00,
         0x0000AA, 0xAA00AA, 0x00AAAA, 0xAAAAAA,
     };
 
     public static final int[] DIM_COLORS = {
         0x000000, 0x550000, 0x005500, 0x555500,
         0x000055, 0x550055, 0x005555, 0x555555,
     };
 
     public static final int[] COLORS_256 = {
         // 0-7: Normal ANSI colors (must match COLORS)
         0x000000, 0xAA0000, 0x00AA00, 0xAAAA00, 0x0000AA, 0xAA00AA, 0x00AAAA, 0xAAAAAA,
         // 8-15: Bright ANSI colors (must match BRIGHT_COLORS)
@@ -43,13 +43,13 @@
         0xafd7d7, 0xafd7ff, 0xafff00, 0xafff5f, 0xafff87, 0xafffaf, 0xafffd7, 0xafffff,
         0xd70000, 0xd7005f, 0xd70087, 0xd700af, 0xd700d7, 0xd700ff, 0xd75f00, 0xd75f5f,
         0xd75f87, 0xd75faf, 0xd75fd7, 0xd75fff, 0xd78700, 0xd7875f, 0xd78787, 0xd787af,
-        0xd787d7, 0xd787ff, 0xdfaf00, 0xdfaf5f, 0xdfaf87, 0xdfafaf, 0xdfafdf, 0xdfafff,
-        0xdfdf00, 0xdfdf5f, 0xdfdf87, 0xdfdfaf, 0xdfdfdf, 0xdfdfff, 0xdfff00, 0xdfff5f,
-        0xdfff87, 0xdfffaf, 0xdfffdf, 0xdfffff, 0xff0000, 0xff005f, 0xff0087, 0xff00af,
-        0xff00df, 0xff00ff, 0xff5f00, 0xff5f5f, 0xff5f87, 0xff5faf, 0xff5fdf, 0xff5fff,
-        0xff8700, 0xff875f, 0xff8787, 0xff87af, 0xff87df, 0xff87ff, 0xffaf00, 0xffaf5f,
-        0xffaf87, 0xffafaf, 0xffafdf, 0xffafff, 0xffdf00, 0xffdf5f, 0xffdf87, 0xffdfaf,
-        0xffdfdf, 0xffdfff, 0xffff00, 0xffff5f, 0xffff87, 0xffffaf, 0xffffdf, 0xffffff,
+        0xd787d7, 0xd787ff, 0xd7af00, 0xd7af5f, 0xd7af87, 0xd7afaf, 0xd7afd7, 0xd7afff,
+        0xd7d700, 0xd7d75f, 0xd7d787, 0xd7d7af, 0xd7d7d7, 0xd7d7ff, 0xd7ff00, 0xd7ff5f,
+        0xd7ff87, 0xd7ffaf, 0xd7ffd7, 0xd7ffff, 0xff0000, 0xff005f, 0xff0087, 0xff00af,
+        0xff00d7, 0xff00ff, 0xff5f00, 0xff5f5f, 0xff5f87, 0xff5faf, 0xff5fd7, 0xff5fff,
+        0xff8700, 0xff875f, 0xff8787, 0xff87af, 0xff87d7, 0xff87ff, 0xffaf00, 0xffaf5f,
+        0xffaf87, 0xffafaf, 0xffafd7, 0xffafff, 0xffd700, 0xffd75f, 0xffd787, 0xffd7af,
+        0xffd7d7, 0xffd7ff, 0xffff00, 0xffff5f, 0xffff87, 0xffffaf, 0xffffd7, 0xffffff,
         0x080808, 0x121212, 0x1c1c1c, 0x262626, 0x303030, 0x3a3a3a, 0x444444, 0x4e4e4e,
         0x585858, 0x626262, 0x6c6c6c, 0x767676, 0x808080, 0x8a8a8a, 0x949494, 0x9e9e9e,
         0xa8a8a8, 0xb2b2b2, 0xbcbcbc, 0xc6c6c6, 0xd0d0d0, 0xdadada, 0xe4e4e4, 0xeeeeee
@@ -128,7 +128,7 @@
             Mode = ColorMode.SIXTEEN_COLOR;
         }
 
         public ColorData(final int r, final int g, final int b, final ColorMode mode) {
             R = r;
             G = g;
             B = b;

src/test/java/li/cil/oc2/common/vm/terminal/TerminalColorsTest.java

@@ -0,0 +1,38 @@
+package li.cil.oc2.common.vm.terminal.color;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class TerminalColorsTest {
+
+    @Test
+    void xterm256PaletteMatchesCanonicalFormula() {
+        // §36 m7: xterm-256 color cube is (16 + 36*r + 6*g + b) with per-channel levels [0x00, 0x5f, 0x87, 0xaf, 0xd7, 0xff].
+        // The COLORS_256 array had 29 mis-typed entries using 0xdf instead of 0xd7 for the level-4 component.
+        // This test checks a few key canonical indices.
+
+        // Level-4 (0xd7) red, level-4 green, level-4 blue (not level-5): index 188 = 16 + 36*4 + 6*4 + 4
+        assertEquals(0xd7d7d7, TerminalColors.COLORS_256[188],
+                "index 188 (R=4,G=4,B=4) should be 0xd7d7d7 (was mis-typed as 0xdfdfdf)");
+
+        // R=4, G=3, B=0: index 178 = 16 + 36*4 + 6*3 + 0
+        assertEquals(0xd7af00, TerminalColors.COLORS_256[178],
+                "index 178 (R=4,G=3,B=0) should be 0xd7af00 (was mis-typed as 0xdfaf00)");
+
+        // R=5, G=5, B=4: index 230 = 16 + 36*5 + 6*5 + 4
+        assertEquals(0xffffd7, TerminalColors.COLORS_256[230],
+                "index 230 (R=5,G=5,B=4) should be 0xffffd7 (was mis-typed as 0xffffdf)");
+
+        // R=5, G=4, B=0: index 220 = 16 + 36*5 + 6*4 + 0
+        assertEquals(0xffd700, TerminalColors.COLORS_256[220],
+                "index 220 (R=5,G=4,B=0) should be 0xffd700 (was mis-typed as 0xffdf00)");
+
+        // Verify no 0xdf entries exist in the cube region (16-231)
+        for (int i = 16; i < 232; i++) {
+            String hex = String.format("%06x", TerminalColors.COLORS_256[i]);
+            assertFalse(hex.contains("df"),
+                    "index " + i + " should not contain 'df' (0xdf is not a valid xterm-256 level component)");
+        }
+    }
+}