In QGIS 2.18.16, I am trying to end up with a final desired color specified in RGB (from a style branding book of a client). The map also contains a hillshade with some transparent grey over top of the polygon colors. When I specify the polygon colors in the RGB I need, predictably the final colors are actually the sum of the RGB value plus the effect of the partially transparent grey hillshade.
Is there a way to correct for this in a predictable way? All I can come up with so far is to trial-and-error adjust the colors via RGB in the presence of the transparent hillshade to get closer to my desired RGB from the style book.