When adjusting the transparency of box plots (in Visualization Properties > Appearance), this should apply only to outlier points and not box itself. Transparency is useful for seeing when multiple points overlap. I'm less interested in making the boxes themselves transparent (unless distribution is also shown). When I have many overlapping points, I have to make chart very transparent, which allows me to see points better, but not boxes anymore. End up having to choose one or the other.
Attached images sort of show this, but in past I had many many outliers and the problem was more pronounced.