diff --git a/pyte/streams.py b/pyte/streams.py
index cd0f51c..4269373 100644
--- a/pyte/streams.py
+++ b/pyte/streams.py
@@ -94,6 +94,7 @@ class Stream:
     }
 
     #: CSI escape sequences -- ``CSI P1;P2;...;Pn <fn>``.
+    # Note that Pn can contain digits or `:`
     csi = {
         esc.ICH: "insert_characters",
         esc.CUU: "cursor_up",
@@ -306,10 +307,14 @@ def create_dispatcher(mapping: Mapping[str, str]) -> Dict[str, Callable[..., Non
                 basic_dispatch[char]()
             elif char == CSI_C1:
                 # All parameters are unsigned, positive decimal integers, with
-                # the most significant digit sent first. Any parameter greater
+                # the most significant digit sent first*. Any parameter greater
                 # than 9999 is set to 9999. If you do not specify a value, a 0
                 # value is assumed.
                 #
+                # *Not entirely true: Some SGR parameters allow `:`-delimited additional
+                # subparameters. These additional subparameters are a list of positive decimal integers
+                # following the above rules.
+                #
                 # .. seealso::
                 #
                 #    `VT102 User Guide <http://vt100.net/docs/vt102-ug/>`_
@@ -318,8 +323,12 @@ def create_dispatcher(mapping: Mapping[str, str]) -> Dict[str, Callable[..., Non
                 #    `VT220 Programmer Ref. <http://vt100.net/docs/vt220-rm/>`_
                 #        For details on the characters valid for use as
                 #        arguments.
+                #
+                #    `XTerm <https://invisible-island.net/xterm/xterm.faq.html#color_by_number>`_
+                #        "Using semicolon was incorrect because [...]"
+                #
                 params = []
-                current = ""
+                param_with_subparameters = [0]
                 private = False
                 while True:
                     char = yield None
@@ -337,17 +346,24 @@ def create_dispatcher(mapping: Mapping[str, str]) -> Dict[str, Callable[..., Non
                         draw(char)
                         break
                     elif char.isdigit():
-                        current += char
+                        digit_value = ord(char) - ord("0")
+                        param_with_subparameters[-1] = min(param_with_subparameters[-1] * 10 + digit_value, 9999)
+                    elif char == ":":
+                        param_with_subparameters.append(0)
                     elif char == "$":
                         # XTerm-specific ESC]...$[a-z] sequences are not
                         # currently supported.
                         yield None
                         break
                     else:
-                        params.append(min(int(current or 0), 9999))
+                        # Note: pyte currently doesn't support subparameters.
+                        # Ideally, we'd update SGR handling to be aware of it.
+                        # That's tracked by <https://github.com/selectel/pyte/issues/179>.
+                        current_param, *_subparameters = param_with_subparameters
+                        params.append(current_param)
 
                         if char == ";":
-                            current = ""
+                            param_with_subparameters = [0]
                         else:
                             if private:
                                 csi_dispatch[char](*params, private=True)
diff --git a/tests/test_stream.py b/tests/test_stream.py
index 7a3ad92..d46ed60 100644
--- a/tests/test_stream.py
+++ b/tests/test_stream.py
@@ -70,6 +70,19 @@ def test_unknown_sequences():
     assert handler.args == (6, 0)
     assert handler.kwargs == {}
 
+def test_csi_param_with_colon_context():
+    handler = argcheck()
+    screen = pyte.Screen(80, 24)
+    screen.debug = handler
+
+    stream = pyte.Stream(screen)
+    stream.feed(ctrl.CSI + "6:4Z")
+    assert handler.count == 1
+    # Note: currently pyte doesn't actually do anything with `:`-delimited context,
+    # which is why the `4` disappears here.
+    assert handler.args == ((6),)
+    assert handler.kwargs == {}
+
 
 def test_non_csi_sequences():
     for cmd, event in pyte.Stream.csi.items():