New answers tagged color
You are both correct, as I have tried many different ways to try to edit the symbology and failed. I've been using NTAD as my substitute and just had to select by attributes out the interstates and highways I wanted to keep.
As @Adam, noted you cannot style the web service layers. However you may download the related year shapefiles from here: National Transportation Atlas Database
That layer is an ArcGIS.com portal item (basically a web service), so you're unable to modify the symbology from how it is presented by ESRI.
Export as PNG (r.out.png) and select Output World File. Load up QGIS and import the PNG file. Upon import you will need to select the Coordinate System and QGIS will read the associated .wld file to georeference the image.
In Settings -> Options, rendering tab you can select the three bands used for RGB rendering. It should be set to 1-2-3. It might be that some exotic Raster files have stored a different color scheme inside.
In layer properties go to Symbology tab. Then choose Categories and Unique Values, Many Fields. Choose your both fields and add values to the table with particular symbol and color to all of your combinations.
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