Added an "approximate_rgb" function.

Also covered 256 colour codes with test. Not 100% sure if those test are
any good though.

blessings/__init__.py

@@ -366,6 +366,29 @@ def _formatting_string(self, formatting):
         """Return a new ``FormattingString`` which implicitly receives my notion of "normal"."""
         return FormattingString(formatting, self.normal)
 
+    def approximate_rgb(self, r, g, b):
+        if self.number_of_colors != 256:
+            return self.color(7)
+
+        if r == g == b:
+            offset = int(r / (256.0 / 24.0))
+            index = 232 + offset
+        else:
+            roundint = lambda n, p: (n + p / 2) / p * p
+
+        # Technically this ought to clamp to 0x5f, 0x87, 0xaf, and 0xd7
+        # rather than 0x33, 0x66, 0x99, and 0xcc, but who the hell came
+        # up with that? Seriously.
+        clamped_r = roundint(r, 0x33)
+        clamped_g = roundint(g, 0x33)
+        clamped_b = roundint(b, 0x33)
+
+        col = clamped_b / 0x33
+        row = clamped_g / 0x33
+        face = clamped_r / 0x33
+        index = 36 * face + 6 * row + col + 16
+
+        return self.color(index)
 
 def derivative_colors(colors):
     """Return the names of valid color variants, given the base colors."""

blessings/tests.py

@@ -14,9 +14,10 @@
 from functools import partial
 from StringIO import StringIO
 import sys
+import os
 
 from nose import SkipTest
-from nose.tools import eq_
+from nose.tools import eq_, assert_in
 
 # This tests that __all__ is correct, since we use below everything that should
 # be imported:
@@ -254,3 +255,29 @@ def test_force_styling_none():
     """If ``force_styling=None`` is passed to the constructor, don't ever do styling."""
     t = TestTerminal(force_styling=None)
     eq_(t.save, '')
+
+
+def test_256color():
+    """Test 256 Color Support"""
+    if os.name != "posix":
+        # Blatantly assuming this won't work on non-posix systems.
+        raise SkipTest
+
+    t = TestTerminal()
+
+    for x in range(8):
+        assert_in(unicode(x + 30), t.color(x))
+
+    for x in range(8):
+        assert_in(unicode(x + 90), t.color(x + 8))
+
+    for x in range(16, 255):
+        assert_in(unicode(x), t.color(x))
+
+
+def test_approximate_color():
+    """Test Approximate Colors"""
+    t = TestTerminal()
+    assert_in(u'196m', t.approximate_rgb(255, 0, 0))
+    assert_in(u'46m', t.approximate_rgb(0, 255, 0))
+    assert_in(u'21m', t.approximate_rgb(0, 0, 255))