[Fix] Always respect user-specified color_continuous_scale

CHANGELOG.md

@@ -4,6 +4,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
+### Fixed
+- Fix issue where user-specified `color_continuous_scale` was ignored when template had `autocolorscale=True` [[#5439](https://github.com/plotly/plotly.py/pull/5439)]
+
 ### Updated
 - Speed up `validate_gantt` function [[#5386](https://github.com/plotly/plotly.py/pull/5386)], with thanks to @misrasaurabh1 for the contribution!
 

plotly/express/_core.py

@@ -2486,6 +2486,11 @@ def get_groups_and_orders(args, grouper):
 def make_figure(args, constructor, trace_patch=None, layout_patch=None):
     trace_patch = trace_patch or {}
     layout_patch = layout_patch or {}
+    # Track if color_continuous_scale was explicitly provided by user
+    # (before apply_default_cascade fills it from template/defaults)
+    user_provided_colorscale = (
+        "color_continuous_scale" in args and args["color_continuous_scale"] is not None
+    )
     apply_default_cascade(args)
 
     args = build_dataframe(args, constructor)
@@ -2704,7 +2709,7 @@ def make_figure(args, constructor, trace_patch=None, layout_patch=None):
         range_color = args["range_color"] or [None, None]
 
         colorscale_validator = ColorscaleValidator("colorscale", "make_figure")
-        layout_patch["coloraxis1"] = dict(
+        coloraxis_dict = dict(
             colorscale=colorscale_validator.validate_coerce(
                 args["color_continuous_scale"]
             ),
@@ -2715,6 +2720,11 @@ def make_figure(args, constructor, trace_patch=None, layout_patch=None):
                 title_text=get_decorated_label(args, args[colorvar], colorvar)
             ),
         )
+        # Set autocolorscale=False if user explicitly provided colorscale. Otherwise a template
+        # that sets autocolorscale=True would override the user provided colorscale.
+        if user_provided_colorscale:
+            coloraxis_dict["autocolorscale"] = False
+        layout_patch["coloraxis1"] = coloraxis_dict
     for v in ["height", "width"]:
         if args[v]:
             layout_patch[v] = args[v]

plotly/express/_imshow.py

@@ -233,6 +233,11 @@ def imshow(
     axes labels and ticks.
     """
     args = locals()
+    # Track if color_continuous_scale was explicitly provided by user
+    # (before apply_default_cascade fills it from template/defaults)
+    user_provided_colorscale = (
+        "color_continuous_scale" in args and args["color_continuous_scale"] is not None
+    )
     apply_default_cascade(args)
     labels = labels.copy()
     nslices_facet = 1
@@ -419,14 +424,19 @@ def imshow(
             layout["xaxis"] = dict(scaleanchor="y", constrain="domain")
             layout["yaxis"]["constrain"] = "domain"
         colorscale_validator = ColorscaleValidator("colorscale", "imshow")
-        layout["coloraxis1"] = dict(
+        coloraxis_dict = dict(
             colorscale=colorscale_validator.validate_coerce(
                 args["color_continuous_scale"]
             ),
             cmid=color_continuous_midpoint,
             cmin=zmin,
             cmax=zmax,
         )
+        # Set autocolorscale=False if user explicitly provided colorscale. Otherwise a template
+        # that sets autocolorscale=True would override the user provided colorscale.
+        if user_provided_colorscale:
+            coloraxis_dict["autocolorscale"] = False
+        layout["coloraxis1"] = coloraxis_dict
         if labels["color"]:
             layout["coloraxis1"]["colorbar"] = dict(title_text=labels["color"])
 

tests/test_optional/test_px/test_colors.py

@@ -60,3 +60,24 @@ def test_color_categorical_dtype():
     px.scatter(
         df[df.day != df.day.cat.categories[0]], x="total_bill", y="tip", color="day"
     )
+
+
+def test_color_continuous_scale_autocolorscale():
+    # User-provided colorscale should override template autocolorscale=True
+    fig = px.scatter(
+        x=[1, 2],
+        y=[1, 2],
+        color=[1, 2],
+        color_continuous_scale="Viridis",
+        template=dict(layout_coloraxis_autocolorscale=True),
+    )
+    assert fig.layout.coloraxis1.autocolorscale is False
+
+    # Without user-provided colorscale, template autocolorscale should be respected
+    fig2 = px.scatter(
+        x=[1, 2],
+        y=[1, 2],
+        color=[1, 2],
+        template=dict(layout_coloraxis_autocolorscale=True),
+    )
+    assert fig2.layout.coloraxis1.autocolorscale is None

tests/test_optional/test_px/test_imshow.py

@@ -98,6 +98,23 @@ def test_colorscale():
     assert fig.layout.coloraxis1.colorscale[0] == (0.0, "#440154")
 
 
+def test_imshow_color_continuous_scale_autocolorscale():
+    # User-provided colorscale should override template autocolorscale=True
+    fig = px.imshow(
+        img_gray,
+        color_continuous_scale="Viridis",
+        template=dict(layout_coloraxis_autocolorscale=True),
+    )
+    assert fig.layout.coloraxis1.autocolorscale is False
+
+    # Without user-provided colorscale, template autocolorscale should be respected
+    fig2 = px.imshow(
+        img_gray,
+        template=dict(layout_coloraxis_autocolorscale=True),
+    )
+    assert fig2.layout.coloraxis1.autocolorscale is None
+
+
 def test_wrong_dimensions():
     imgs = [1, np.ones((5,) * 3), np.ones((5,) * 4)]
     msg = "px.imshow only accepts 2D single-channel, RGB or RGBA images."