Custom color ramps in MapViewer

[FourCornersMapping]

I would like the ability to customize color ramps in ArcGIS Online Map Viewer. I would like to be able to set the colors, control stops, and transparency of stops, an easy feat in ArcGIS Pro. This would have utility if, for instance, I wanted to make higher elevations appear snowy/white. Here is an attempt in Map Viewer without being able to control the colors and stops of the ramp:

And here is a version in Pro being able to set a 100% transparent white to 0% transparent white color ramp: