undo: back out the color condition check as it still makes the cartes…

…ian plot draw unexpectedly

src/stack.ts

@@ -182,7 +182,7 @@ export function stack(m: Mark | MarkDef, encoding: Encoding<string>): StackPrope
     // TBD: we should only enter this branch if there's also a "color" and maybe a group channel?
     const isPolar = isPolarPositionChannel(fieldChannel) || isPolarPositionChannel(dimensionChannel);
 
-    if (!hasSameDimensionAndStackedField && (isPolar ? dimensionChannel === fieldChannel || encoding['color'] : true)) {
+    if (!hasSameDimensionAndStackedField && (isPolar ? dimensionChannel === fieldChannel : true)) {
       // avoid grouping by the stacked field
       // TKTK: find out why
       groupbyChannels.push(dimensionChannel);