I have used the JSON format successfully for symbology in the past, but this is the first time I've used something besides solid or null for the fill. For this project I wanted a diagonal line. I defined it in JSON format as
var myfill = new SimpleFillSymbol({
"type": "esriSFS",
"style": "esriSFSForwardDiagonal",
"color": [255, 0, 0, 255],
"outline": {
"type": "esriSLS",
"style": "esriSLSSolid",
"color": [255, 0, 0, 130],
"width": 3
}
})

I expected the diagonal lines to be red, but they are black. The red outline is correct. I've tried 3.14 and 3.15 and got the same results.
What gives? I'm following the syntax for symbol objects found in ArcGIS REST API