diff --git a/plotly_express/_core.py b/plotly_express/_core.py
index 20e05c5..9c7ea9e 100644
--- a/plotly_express/_core.py
+++ b/plotly_express/_core.py
@@ -1,5 +1,6 @@
 import plotly.graph_objs as go
 from plotly.offline import init_notebook_mode, iplot
+import plotly.io as pio
 from collections import namedtuple, OrderedDict
 from .colors import qualitative, sequential
 import math
@@ -7,15 +8,15 @@
 
 class PxDefaults(object):
     def __init__(self):
-        self.color_discrete_sequence = qualitative.Plotly
-        self.color_continuous_scale = sequential.Plasma
+        self.template = None
+        self.width = None
+        self.height = 600
+        self.color_discrete_sequence = None
+        self.color_continuous_scale = None
         self.symbol_sequence = ["circle", "diamond", "square", "x", "cross"]
         self.line_dash_sequence = ["solid", "dot", "dash", "longdash", "dashdot"] + [
             "longdashdot"
         ]
-        self.template = "plotly"
-        self.width = None
-        self.height = 600
         self.size_max = 20
 
 
@@ -569,7 +570,7 @@ def make_trace_spec(args, constructor, attrs, trace_patch):
             if "color" in attrs:
                 if "marker" not in trace_spec.trace_patch:
                     trace_spec.trace_patch["marker"] = dict()
-                first_default_color = defaults.color_discrete_sequence[0]
+                first_default_color = args["color_discrete_sequence"][0]
                 trace_spec.trace_patch["marker"]["color"] = first_default_color
             result.append(trace_spec)
     if "trendline" in args and args["trendline"]:
@@ -588,7 +589,8 @@ def one_group(x):
     return ""
 
 
-def infer_config(args, constructor, trace_patch):
+def apply_default_cascade(args):
+    # first we apply px.defaults to unspecified args
     for param in (
         ["color_discrete_sequence", "color_continuous_scale"]
         + ["symbol_sequence", "line_dash_sequence", "template"]
@@ -597,6 +599,43 @@ def infer_config(args, constructor, trace_patch):
         if param in args and args[param] is None:
             args[param] = getattr(defaults, param)
 
+    # load the default template if set, otherwise "plotly"
+    if args["template"] is None:
+        if pio.templates.default is not None:
+            args["template"] = pio.templates.default
+        else:
+            args["template"] = "plotly"
+
+    # retrieve the actual template if we were given a name
+    try:
+        template = pio.templates[args["template"]]
+    except Exception:
+        template = args["template"]
+
+    # if colors not set explicitly or in px.defaults, defer to a template
+    # if the template doesn't have one, we set some final fallback defaults
+    if "color_continuous_scale" in args:
+        if args["color_continuous_scale"] is None:
+            try:
+                args["color_continuous_scale"] = [
+                    x[1] for x in template.layout.colorscale.sequential
+                ]
+            except AttributeError:
+                pass
+        if args["color_continuous_scale"] is None:
+            args["color_continuous_scale"] = sequential.Plasma
+
+    if "color_discrete_sequence" in args:
+        if args["color_discrete_sequence"] is None:
+            try:
+                args["color_discrete_sequence"] = template.layout.colorway
+            except AttributeError:
+                pass
+        if args["color_discrete_sequence"] is None:
+            args["color_discrete_sequence"] = qualitative.Plotly
+
+
+def infer_config(args, constructor, trace_patch):
     attrables = (
         ["x", "y", "z", "a", "b", "c", "r", "theta", "size"]
         + ["dimensions", "hover_name", "hover_data", "text", "error_x", "error_x_minus"]
@@ -631,9 +670,7 @@ def infer_config(args, constructor, trace_patch):
 
     sizeref = 0
     if "size" in args and args["size"]:
-        sizeref = args["data_frame"][args["size"]].max() / (
-            args["size_max"] * args["size_max"]
-        )
+        sizeref = args["data_frame"][args["size"]].max() / args["size_max"] ** 2
 
     color_range = None
     if "color" in args:
@@ -702,6 +739,7 @@ def infer_config(args, constructor, trace_patch):
 
 
 def make_figure(args, constructor, trace_patch={}, layout_patch={}):
+    apply_default_cascade(args)
     trace_specs, grouped_mappings, sizeref, color_range = infer_config(
         args, constructor, trace_patch
     )