When creating a legend in Plato or PackEdge, the colour of the legend is often setup as a technical ink so that it shows up consistently and users are not confused by which colours are being used in the artwork and what colours belong to the legend.
One limitation of creating the legend out of technical ink is that it is not possible for a technical ink to be screened (i.e., coloured 50% or used in a grad). Sometimes, users would like to see their logo which may sometimes have screened areas or gradients.
As a solution to this default behavior, it is possible to create a Bitmap TIFF image in Adobe® Photoshop® and then use the bitmap TIFF image in a Normalized PDF to create an Image mark that has the appearance that the technical ink is screened. This will satisfy the application's desire to have all technical inks at 100% and achieve the results you require.