diff --git a/core/fxge/skia/fx_skia_device.cpp b/core/fxge/skia/fx_skia_device.cpp
index 5a7a047..c4040ae 100644
--- a/core/fxge/skia/fx_skia_device.cpp
+++ b/core/fxge/skia/fx_skia_device.cpp
@@ -287,6 +287,11 @@
 #endif  // DRAW_SKIA_CLIP
 
 #if defined(_SKIA_SUPPORT_)
+bool IsRGBColorGrayScale(uint32_t color) {
+  return FXARGB_R(color) == FXARGB_G(color) &&
+         FXARGB_R(color) == FXARGB_B(color);
+}
+
 static void DebugValidate(const RetainPtr<CFX_DIBitmap>& bitmap,
                           const RetainPtr<CFX_DIBitmap>& device) {
   if (bitmap) {
@@ -680,31 +685,45 @@
   int rowBytes = pSource->GetPitch();
   switch (pSource->GetBPP()) {
     case 1: {
-      dst8_storage = DataVector<uint8_t>(Fx2DSizeOrDie(width, height));
-      pdfium::span<uint8_t> dst8_pixels(dst8_storage);
       // By default, the two colors for grayscale are 0xFF and 0x00 unless they
       // are specified in the palette.
-      uint8_t color1 = 0x00;
-      uint8_t color2 = 0xFF;
+      uint8_t color0 = 0x00;
+      uint8_t color1 = 0xFF;
+      bool use_two_colors = true;
       if (pSource->GetFormat() == FXDIB_Format::k1bppRgb &&
           pSource->HasPalette()) {
-        color1 = FXARGB_R(pSource->GetPaletteArgb(0));
-        color2 = FXARGB_R(pSource->GetPaletteArgb(1));
-        DCHECK_EQ(color1, FXARGB_G(pSource->GetPaletteArgb(0)));
-        DCHECK_EQ(color1, FXARGB_B(pSource->GetPaletteArgb(0)));
-        DCHECK_EQ(color2, FXARGB_G(pSource->GetPaletteArgb(1)));
-        DCHECK_EQ(color2, FXARGB_B(pSource->GetPaletteArgb(1)));
+        // When `pSource` has 1 bit per pixel, its palette will contain 2
+        // colors, and the R,G,B channels of either color will have equal
+        // values. However, there are cases that R,G,B are not all the same and
+        // these 2 colors stand for the boundaries of a range of colors to be
+        // used for bitmap rendering. We need to handle the color palette
+        // differently depending on these conditions.
+        uint32_t palette_color0 = pSource->GetPaletteArgb(0);
+        uint32_t palette_color1 = pSource->GetPaletteArgb(1);
+        use_two_colors = IsRGBColorGrayScale(palette_color0) &&
+                         IsRGBColorGrayScale(palette_color1);
+        if (use_two_colors) {
+          color0 = FXARGB_R(palette_color0);
+          color1 = FXARGB_R(palette_color1);
+        }
+
+        // TODO(pdfium:1810): Handle upsampling when a range of colors (more
+        // than 2 colors) are provided in the source palette.
       }
 
-      for (int y = 0; y < height; ++y) {
-        const uint8_t* srcRow =
-            static_cast<const uint8_t*>(buffer) + y * rowBytes;
-        pdfium::span<uint8_t> dst_row = dst8_pixels.subspan(y * width);
-        for (int x = 0; x < width; ++x)
-          dst_row[x] = srcRow[x >> 3] & (1 << (~x & 0x07)) ? color2 : color1;
+      if (use_two_colors) {
+        dst8_storage = DataVector<uint8_t>(Fx2DSizeOrDie(width, height));
+        pdfium::span<uint8_t> dst8_pixels(dst8_storage);
+        for (int y = 0; y < height; ++y) {
+          const uint8_t* srcRow =
+              static_cast<const uint8_t*>(buffer) + y * rowBytes;
+          pdfium::span<uint8_t> dst_row = dst8_pixels.subspan(y * width);
+          for (int x = 0; x < width; ++x)
+            dst_row[x] = srcRow[x >> 3] & (1 << (~x & 0x07)) ? color1 : color0;
+        }
+        buffer = dst8_storage.data();
+        rowBytes = width;
       }
-      buffer = dst8_storage.data();
-      rowBytes = width;
       break;
     }
     case 8: