diff --git a/scripts/r.colors.stddev/tests/r_colors_stddev_test.py b/scripts/r.colors.stddev/tests/r_colors_stddev_test.py
new file mode 100644
index 00000000000..79c26c11607
--- /dev/null
+++ b/scripts/r.colors.stddev/tests/r_colors_stddev_test.py
@@ -0,0 +1,47 @@
+"""Tests of r.colors.stddev"""
+
+import statistics
+
+import pytest
+
+from grass.tools import Tools
+
+# data = col() over a one-row, nine-column region holds the values 1..9.
+VALUES = range(1, 10)
+MEAN = statistics.fmean(VALUES)  # 5.0
+STDDEV = statistics.pstdev(VALUES)  # population stddev, as reported by r.univar
+# The rule values are written with six-decimal formatting, so compare loosely.
+TOL = 1e-3
+
+
+def colors_of(session):
+    """Return a Tools session holding a raster "data" with values 1..9."""
+    tools = Tools(session=session)
+    tools.g_region(n=1, s=0, w=0, e=9, res=1)
+    tools.r_mapcalc(expression="data = col()")
+    return tools
+
+
+def test_default_rules_center_on_mean(xy_raster_dataset_session_mapset):
+    """Default mode: white at the mean, blue at mean - 2*stddev, red at mean + 2*stddev."""
+    tools = colors_of(xy_raster_dataset_session_mapset)
+    tools.r_colors_stddev(map="data")
+    table = tools.r_colors_out(map="data", format="json").json["table"]
+    white = [e["value"] for e in table if e["color"] == "#FFFFFF"]
+    blue = [e["value"] for e in table if e["color"] == "#0000FF"]
+    red = [e["value"] for e in table if e["color"] == "#FF0000"]
+    assert white == [pytest.approx(MEAN, abs=TOL)]
+    assert blue == [pytest.approx(MEAN - 2 * STDDEV, abs=TOL)]
+    assert any(v == pytest.approx(MEAN + 2 * STDDEV, abs=TOL) for v in red)
+
+
+def test_bands_green_brackets_mean(xy_raster_dataset_session_mapset):
+    """Banded mode (-b): the central green band spans mean +/- one stddev."""
+    tools = colors_of(xy_raster_dataset_session_mapset)
+    tools.r_colors_stddev(map="data", flags="b")
+    table = tools.r_colors_out(map="data", format="json").json["table"]
+    green = sorted(e["value"] for e in table if e["color"] == "#00FF00")
+    assert green == [
+        pytest.approx(MEAN - STDDEV, abs=TOL),
+        pytest.approx(MEAN + STDDEV, abs=TOL),
+    ]