Handle named colors as string in equal operator

src/ol/style/expressions.js

@@ -606,6 +606,12 @@ function getEqualOperator(operator) {
         );
       }
 
+      if (type === (ValueTypes.COLOR | ValueTypes.STRING)) {
+        // It's not possible to compare attributes with color values
+        // So force it to be treated as a string
+        type = ValueTypes.STRING;
+      }
+
       return `(${expressionToGlsl(
         context,
         args[0],

test/browser/spec/ol/style/expressions.test.js

@@ -250,6 +250,9 @@ describe('ol.style.expressions', function () {
       expect(expressionToGlsl(context, ['==', 10, ['get', 'attr4']])).to.eql(
         '(10.0 == a_attr4)'
       );
+      expect(expressionToGlsl(context, ['==', 'red', ['get', 'attr4']])).to.eql(
+        '(0.0 == a_attr4)'
+      );
       expect(expressionToGlsl(context, ['!=', 10, ['get', 'attr4']])).to.eql(
         '(10.0 != a_attr4)'
       );