I was looking for an answer to an issue with Acrobat DC and how to Highlight Irregular Shapes. I found the same question asked at https://answers.acrobatusers.com/color-fill-questions-q64895.aspx
I have now found the answer … use the “Cloud” tool on the “Comments” tool bar. Then edit the properties to remove the border and adjust the fill.
Hope this helps others. Rds