diff --git a/Tests/test_file_gif.py b/Tests/test_file_gif.py
index d571692b1..3c2e96356 100644
--- a/Tests/test_file_gif.py
+++ b/Tests/test_file_gif.py
@@ -205,14 +205,14 @@ def test_optimize_full_l():
 
 
 def test_optimize_if_palette_can_be_reduced_by_half():
-    with Image.open("Tests/images/test.colors.gif") as im:
-        # Reduce dimensions because original is too big for _get_optimize()
-        im = im.resize((591, 443))
-    im_rgb = im.convert("RGB")
+    im = Image.new("P", (8, 1))
+    im.palette = ImagePalette.raw("RGB", bytes((0, 0, 0) * 150))
+    for i in range(8):
+        im.putpixel((i, 0), (i + 1, 0, 0))
 
     for optimize, colors in ((False, 256), (True, 8)):
         out = BytesIO()
-        im_rgb.save(out, "GIF", optimize=optimize)
+        im.save(out, "GIF", optimize=optimize)
         with Image.open(out) as reloaded:
             assert len(reloaded.palette.palette) // 3 == colors
 
@@ -1180,18 +1180,17 @@ def test_palette_save_L(tmp_path):
 
 
 def test_palette_save_P(tmp_path):
-    # Pass in a different palette, then construct what the image would look like.
-    # Forcing a non-straight grayscale palette.
-
-    im = hopper("P")
-    palette = bytes(255 - i // 3 for i in range(768))
+    im = Image.new("P", (1, 2))
+    im.putpixel((0, 1), 1)
 
     out = str(tmp_path / "temp.gif")
-    im.save(out, palette=palette)
+    im.save(out, palette=bytes((1, 2, 3, 4, 5, 6)))
 
     with Image.open(out) as reloaded:
-        im.putpalette(palette)
-        assert_image_equal(reloaded, im)
+        reloaded_rgb = reloaded.convert("RGB")
+
+        assert reloaded_rgb.getpixel((0, 0)) == (1, 2, 3)
+        assert reloaded_rgb.getpixel((0, 1)) == (4, 5, 6)
 
 
 def test_palette_save_duplicate_entries(tmp_path):
diff --git a/Tests/test_image.py b/Tests/test_image.py
index b9c57770c..83dac7080 100644
--- a/Tests/test_image.py
+++ b/Tests/test_image.py
@@ -638,8 +638,8 @@ class TestImage:
                 im.remap_palette(None)
 
     def test_remap_palette_transparency(self):
-        im = Image.new("P", (1, 2))
-        im.putpixel((0, 1), 1)
+        im = Image.new("P", (1, 2), (0, 0, 0))
+        im.putpixel((0, 1), (255, 0, 0))
         im.info["transparency"] = 0
 
         im_remapped = im.remap_palette([1, 0])
diff --git a/Tests/test_image_convert.py b/Tests/test_image_convert.py
index 01a182cf1..f5775f09c 100644
--- a/Tests/test_image_convert.py
+++ b/Tests/test_image_convert.py
@@ -117,11 +117,11 @@ def test_trns_p(tmp_path):
     f = str(tmp_path / "temp.png")
 
     im_l = im.convert("L")
-    assert im_l.info["transparency"] == 1  # undone
+    assert im_l.info["transparency"] == 0
     im_l.save(f)
 
     im_rgb = im.convert("RGB")
-    assert im_rgb.info["transparency"] == (0, 1, 2)  # undone
+    assert im_rgb.info["transparency"] == (0, 0, 0)
     im_rgb.save(f)
 
 
diff --git a/Tests/test_image_putpalette.py b/Tests/test_image_putpalette.py
index 665e08a7e..376553344 100644
--- a/Tests/test_image_putpalette.py
+++ b/Tests/test_image_putpalette.py
@@ -84,3 +84,14 @@ def test_rgba_palette(mode, palette):
     im.putpalette(palette, mode)
     assert im.getpalette() == [1, 2, 3]
     assert im.palette.colors == {(1, 2, 3, 4): 0}
+
+
+def test_empty_palette():
+    im = Image.new("P", (1, 1))
+    assert im.getpalette() == []
+
+
+def test_undefined_palette_index():
+    im = Image.new("P", (1, 1), 3)
+    im.putpalette((1, 2, 3))
+    assert im.convert("RGB").getpixel((0, 0)) == (0, 0, 0)
diff --git a/src/PIL/BlpImagePlugin.py b/src/PIL/BlpImagePlugin.py
index 31373a532..398696d5c 100644
--- a/src/PIL/BlpImagePlugin.py
+++ b/src/PIL/BlpImagePlugin.py
@@ -419,9 +419,11 @@ class BLPEncoder(ImageFile.PyEncoder):
     def _write_palette(self):
         data = b""
         palette = self.im.getpalette("RGBA", "RGBA")
-        for i in range(256):
+        for i in range(len(palette) // 4):
             r, g, b, a = palette[i * 4 : (i + 1) * 4]
             data += struct.pack("<4B", b, g, r, a)
+        while len(data) < 256 * 4:
+            data += b"\x00" * 4
         return data
 
     def encode(self, bufsize):
diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index 244d2e435..69c7c506b 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -1074,7 +1074,7 @@ class Image:
         if mode == "P" and palette != Palette.ADAPTIVE:
             from . import ImagePalette
 
-            new_im.palette = ImagePalette.ImagePalette("RGB", list(range(256)) * 3)
+            new_im.palette = ImagePalette.ImagePalette("RGB", im.getpalette("RGB"))
         if delete_trns:
             # crash fail if we leave a bytes transparency in an rgb/l mode.
             del new_im.info["transparency"]
diff --git a/src/libImaging/Convert.c b/src/libImaging/Convert.c
index 7fe24a639..7677a81f7 100644
--- a/src/libImaging/Convert.c
+++ b/src/libImaging/Convert.c
@@ -1295,7 +1295,6 @@ topalette(
     int alpha;
     int x, y;
     ImagingPalette palette = inpalette;
-    ;
 
     /* Map L or RGB/RGBX/RGBA to palette image */
     if (strcmp(imIn->mode, "L") != 0 && strncmp(imIn->mode, "RGB", 3) != 0) {
@@ -1307,7 +1306,14 @@ topalette(
     if (palette == NULL) {
         /* FIXME: make user configurable */
         if (imIn->bands == 1) {
-            palette = ImagingPaletteNew("RGB"); /* Initialised to grey ramp */
+            palette = ImagingPaletteNew("RGB");
+
+            palette->size = 256;
+            int i;
+            for (i = 0; i < 256; i++) {
+                palette->palette[i * 4] = palette->palette[i * 4 + 1] =
+                    palette->palette[i * 4 + 2] = (UINT8)i;
+            }
         } else {
             palette = ImagingPaletteNewBrowser(); /* Standard colour cube */
         }
diff --git a/src/libImaging/Palette.c b/src/libImaging/Palette.c
index 71a095c2c..059d7b72a 100644
--- a/src/libImaging/Palette.c
+++ b/src/libImaging/Palette.c
@@ -39,11 +39,8 @@ ImagingPaletteNew(const char *mode) {
     strncpy(palette->mode, mode, IMAGING_MODE_LENGTH - 1);
     palette->mode[IMAGING_MODE_LENGTH - 1] = 0;
 
-    /* Initialize to ramp */
-    palette->size = 256;
+    palette->size = 0;
     for (i = 0; i < 256; i++) {
-        palette->palette[i * 4 + 0] = palette->palette[i * 4 + 1] =
-            palette->palette[i * 4 + 2] = (UINT8)i;
         palette->palette[i * 4 + 3] = 255; /* opaque */
     }
 
@@ -62,16 +59,10 @@ ImagingPaletteNewBrowser(void) {
         return NULL;
     }
 
-    /* Blank out unused entries */
     /* FIXME: Add 10-level windows palette here? */
 
-    for (i = 0; i < 10; i++) {
-        palette->palette[i * 4 + 0] = palette->palette[i * 4 + 1] =
-            palette->palette[i * 4 + 2] = 0;
-    }
-
     /* Simple 6x6x6 colour cube */
-
+    i = 10;
     for (b = 0; b < 256; b += 51) {
         for (g = 0; g < 256; g += 51) {
             for (r = 0; r < 256; r += 51) {
@@ -82,15 +73,10 @@ ImagingPaletteNewBrowser(void) {
             }
         }
     }
+    palette->size = i;
 
-    /* Blank out unused entries */
     /* FIXME: add 30-level greyscale wedge here? */
 
-    for (; i < 256; i++) {
-        palette->palette[i * 4 + 0] = palette->palette[i * 4 + 1] =
-            palette->palette[i * 4 + 2] = 0;
-    }
-
     return palette;
 }
 
diff --git a/src/libImaging/Quant.c b/src/libImaging/Quant.c
index 02a4a5c76..c84acb998 100644
--- a/src/libImaging/Quant.c
+++ b/src/libImaging/Quant.c
@@ -1825,6 +1825,7 @@ ImagingQuantize(Imaging im, int colors, int mode, int kmeans) {
 
         free(newData);
 
+        imOut->palette->size = (int)paletteLength;
         pp = imOut->palette->palette;
 
         for (i = j = 0; i < (int)paletteLength; i++) {
@@ -1832,16 +1833,9 @@ ImagingQuantize(Imaging im, int colors, int mode, int kmeans) {
             *pp++ = palette[i].c.g;
             *pp++ = palette[i].c.b;
             if (withAlpha) {
-                *pp++ = palette[i].c.a;
-            } else {
-                *pp++ = 255;
+                *pp = palette[i].c.a;
             }
-        }
-        for (; i < 256; i++) {
-            *pp++ = 0;
-            *pp++ = 0;
-            *pp++ = 0;
-            *pp++ = 255;
+            pp++;
         }
 
         if (withAlpha) {