diff --git a/Lib/idlelib/colorizer.py b/Lib/idlelib/colorizer.py
index 7a919f164fc..ff408452880 100644
--- a/Lib/idlelib/colorizer.py
+++ b/Lib/idlelib/colorizer.py
@@ -21,8 +21,7 @@ def make_pat():
     # 1st 'file' colorized normal, 2nd as builtin, 3rd as string
     builtin = r"([^.'\"\\#]\b|^)" + any("BUILTIN", builtinlist) + r"\b"
     comment = any("COMMENT", [r"#[^\n]*"])
-    stringprefix = (r"(\br|R|u|U|f|F|fr|Fr|fR|FR|rf|rF|Rf|RF"
-                    "|b|B|br|Br|bR|BR|rb|rB|Rb|RB)?")
+    stringprefix = r"(?i:\br|u|f|fr|rf|b|br|rb)?"
     sqstring = stringprefix + r"'[^'\\\n]*(\\.[^'\\\n]*)*'?"
     dqstring = stringprefix + r'"[^"\\\n]*(\\.[^"\\\n]*)*"?'
     sq3string = stringprefix + r"'''[^'\\]*((\\.|'(?!''))[^'\\]*)*(''')?"
@@ -262,10 +261,11 @@ def _color_delegator(parent):  # htest #
     top = Toplevel(parent)
     top.title("Test ColorDelegator")
     x, y = map(int, parent.geometry().split('+')[1:])
-    top.geometry("600x200+%d+%d" % (x + 100, y + 175))
+    top.geometry("700x250+%d+%d" % (x + 20, y + 175))
     source = ("# Following has syntax errors\n"
         "if True: then int 1\nelif False: print 0\nelse: float(None)\n"
-        "#unicode and byte strings, valid prefixes should be colored\n"
+        "if iF + If + IF: 'keywork matching must respect case'\n"
+        "# All valid prefixes for unicode and byte strings should be colored\n"
         "'x', '''x''', \"x\", \"\"\"x\"\"\"\n"
         "r'x', u'x', R'x', U'x', f'x', F'x', ur'is invalid'\n"
         "fr'x', Fr'x', fR'x', FR'x', rf'x', rF'x', Rf'x', RF'x'\n"