diff --git a/src/plots/plots.js b/src/plots/plots.js
index 38416678886..510b1752550 100644
--- a/src/plots/plots.js
+++ b/src/plots/plots.js
@@ -659,6 +659,51 @@ plots.linkSubplots = function(newFullData, newFullLayout, oldFullData, oldFullLa
     }
 };
 
+// This function clears any trace attributes with valType: color and
+// no set dflt filed in the plot schema. This is needed because groupby (which
+// is the only transform for which this currently applies) supplies parent
+// trace defaults, then expanded trace defaults. The result is that `null`
+// colors are default-supplied and inherited as a color instead of a null.
+// The result is that expanded trace default colors have no effect, with
+// the final result that groups are indistinguishable. This function clears
+// those colors so that individual groupby groups get unique colors.
+plots.clearExpandedTraceDefaultColors = function(trace) {
+    var colorAttrs, path, i;
+
+    // This uses weird closure state in order to satisfy the linter rule
+    // that we can't create functions in a loop.
+    function locateColorAttrs(attr, attrName, attrs, level) {
+        path[level] = attrName;
+        path.length = level + 1;
+        if(attr.valType === 'color' && attr.dflt === undefined) {
+            colorAttrs.push(path.join('.'));
+        }
+    }
+
+    path = [];
+
+    // Get the cached colorAttrs:
+    colorAttrs = trace._module._colorAttrs;
+
+    // Or else compute and cache the colorAttrs on the module:
+    if(!colorAttrs) {
+        trace._module._colorAttrs = colorAttrs = [];
+        PlotSchema.crawl(
+            trace._module.attributes,
+            locateColorAttrs
+        );
+    }
+
+    for(i = 0; i < colorAttrs.length; i++) {
+        var origprop = Lib.nestedProperty(trace, '_input.' + colorAttrs[i]);
+
+        if(!origprop.get()) {
+            Lib.nestedProperty(trace, colorAttrs[i]).set(null);
+        }
+    }
+};
+
+
 plots.supplyDataDefaults = function(dataIn, dataOut, layout, fullLayout) {
     var i, fullTrace, trace;
     var modules = fullLayout._modules = [],
@@ -694,8 +739,8 @@ plots.supplyDataDefaults = function(dataIn, dataOut, layout, fullLayout) {
             var expandedTraces = applyTransforms(fullTrace, dataOut, layout, fullLayout);
 
             for(var j = 0; j < expandedTraces.length; j++) {
-                var expandedTrace = expandedTraces[j],
-                    fullExpandedTrace = plots.supplyTraceDefaults(expandedTrace, cnt, fullLayout, i);
+                var expandedTrace = expandedTraces[j];
+                var fullExpandedTrace = plots.supplyTraceDefaults(expandedTrace, cnt, fullLayout, i);
 
                 // mutate uid here using parent uid and expanded index
                 // to promote consistency between update calls
diff --git a/src/transforms/groupby.js b/src/transforms/groupby.js
index ef1b78426b1..6590c428c26 100644
--- a/src/transforms/groupby.js
+++ b/src/transforms/groupby.js
@@ -10,6 +10,7 @@
 
 var Lib = require('../lib');
 var PlotSchema = require('../plot_api/plot_schema');
+var Plots = require('../plots/plots');
 
 exports.moduleType = 'transform';
 
@@ -172,6 +173,8 @@ function transformOne(trace, state) {
 
         newTrace.name = groupName;
 
+        Plots.clearExpandedTraceDefaultColors(newTrace);
+
         // there's no need to coerce styleLookup[groupName] here
         // as another round of supplyDefaults is done on the transformed traces
         newTrace = Lib.extendDeepNoArrays(newTrace, styleLookup[groupName] || {});
diff --git a/test/jasmine/tests/transform_groupby_test.js b/test/jasmine/tests/transform_groupby_test.js
index 049a2856b5f..734622c0984 100644
--- a/test/jasmine/tests/transform_groupby_test.js
+++ b/test/jasmine/tests/transform_groupby_test.js
@@ -1,4 +1,5 @@
 var Plotly = require('@lib/index');
+var Plots = require('@src/plots/plots');
 var Lib = require('@src/lib');
 
 var createGraphDiv = require('../assets/create_graph_div');
@@ -236,9 +237,38 @@ describe('groupby', function() {
                 done();
             });
         });
+    });
+
+    describe('many-to-many transforms', function() {
+        it('varies the color for each expanded trace', function() {
+            var uniqueColors = {};
+            var dataOut = [];
+            var dataIn = [{
+                y: [1, 2, 3],
+                transforms: [
+                    {type: 'filter', operation: '<', value: 4},
+                    {type: 'groupby', groups: ['a', 'b', 'c']}
+                ]
+            }, {
+                y: [4, 5, 6],
+                transforms: [
+                    {type: 'filter', operation: '<', value: 4},
+                    {type: 'groupby', groups: ['a', 'b', 'b']}
+                ]
+            }];
 
+            Plots.supplyDataDefaults(dataIn, dataOut, {}, {});
+
+            for(var i = 0; i < dataOut.length; i++) {
+                uniqueColors[dataOut[i].marker.color] = true;
+            }
+
+            // Confirm that five total colors exist:
+            expect(Object.keys(uniqueColors).length).toEqual(5);
+        });
     });
 
+
     // these tests can be shortened, once the meaning of edge cases gets clarified
     describe('symmetry/degeneracy testing of one-to-many transforms on arbitrary arrays where there is no grouping (implicit 1):', function() {
         'use strict';
@@ -662,6 +692,39 @@ describe('groupby', function() {
         it('passes with no groups', test(mockData0));
         it('passes with empty groups', test(mockData1));
         it('passes with falsey groups', test(mockData2));
+    });
+
+    describe('expanded trace coloring', function() {
+        it('assigns unique colors to each group', function() {
+            var colors = [];
+            var dataOut = [];
+            var dataIn = [{
+                y: [1, 2, 3],
+                transforms: [
+                    {type: 'filter', operation: '<', value: 4},
+                    {type: 'groupby', groups: ['a', 'b', 'c']}
+                ]
+            }, {
+                y: [4, 5, 6],
+                transforms: [
+                    {type: 'filter', operation: '<', value: 4},
+                    {type: 'groupby', groups: ['a', 'b', 'b']}
+                ]
+            }];
+
+            Plots.supplyDataDefaults(dataIn, dataOut, {}, {});
 
+            for(var i = 0; i < dataOut.length; i++) {
+                colors.push(dataOut[i].marker.color);
+            }
+
+            expect(colors).toEqual([
+                '#1f77b4',
+                '#ff7f0e',
+                '#2ca02c',
+                '#d62728',
+                '#9467bd'
+            ]);
+        });
     });
 });