I have been struggling with this for quite a while, so a quick solution would be awesome.
When I build a web-app using Portal for ArcGIS there are quite a few color options from which to choose. However, I find that if I need to use a light color then it becomes very difficult to see the icons. Here is an example when the web-app colors are dark:
However, if I choose a light color the icons do not adjust accordingly...they remain light:
We have new corporate colors and I'm currently making changes to our web apps to reflect this, but being able to use dark icons in some cases would really help.