Light blue is a freehand-line and green is a straight line. So both line attachment types have problems with transparency. The yellow text-marker and the purple squares (one is transparent, one is not) work fine, as you can see.
Thank you for information. We have revised the WANG specification and have found that WANG specification allows to highlight lines, rectangles and freehands. Current version of SDK supports only highlighting of rectangle annotations. In version 8.5.X we will add the ability to highlight the line-based annotations. I think necessary functionality may be available in 1-2 months.