We have this issue here: Feature layer and map image service attribute-driven symbology related with rendering a feature service based on a map that uses data driven symbology.
We have attributes that store the color of each feature as a hex color and the size as a number. We have tried to find a workaround for the issue by creating a unique renderer with visual variables. It works for the size but we haven't found a way to make it work for colors. The color variable must have stops of numeric values and in our case, we store the color value directly. The colors can be whatever input from the user.
Can we create a custom renderer to change the color of the features based on the value of a field?