Curious: (1) Do you have some screenshots demonstrating this issue and (2) perhaps an example PDF that others could download for the purpose of issue reproduction? (I have not seen this issue, nor am I able to reproduce this issue after repeatedly trying under Preview. I have compared it with on-screen rendering under Acrobat XI, as well.) // Preview 10.0 (944.5), macOS 10.13.4 (17E202), MacBook Pro (13-inch, 2017)