black and white pdfs have color

I'm using a 64-bit Windows 7 OS to print from AutoCAD to adobe PDFs. When printing from AutoCAD we use a specific color palette file with which to print specific lineweights associated with the colors that are already programmed into our PDF presets. The color palette we use has always been black and white until I recently updated my registered version of Acrobat DC and now can see random lines of color in the PDFs that are supposed to be B/W. Before the Acrobat update I still saw black and white on my computer but my associates saw the color and then informed me as we send these document sets to clients. When I zoom in, they almost completely disappear, and sometimes appear again after zooming back out. When we print these PDFs, they are black and white as expected, but there continue to be lines of color (usually blue or yellow) in our digital PDFs. All suggestions welcome. Help please.