The activity is the App_Integration.PDF.WatermarkPDF, and one of the boxes is the XColor, here I have tried with:
pdfsharp.Drawing.XColor.FromArgb(212, 224, 240), pdfsharp.Drawing.XColor.FromGrayScale(0.9)
But none of these is changing the Color of the Watermark.
I founded another post here regarding to this, and I am very grateful for the answers founded here, but it does not answer my doubt.
The Watermark PDF activity is set to use a fixed color instead of using the color which we pass as an argument. You can create your own custom activity to use the dynamic color value. See the Screenshot.