Hi i woud like to know how to remove these black dots on some boards. There are chips under it right!

Hi everybody. I have a green palladium solution. I took a sample of it and I added a DMG and sodium hydroxide solution to the green pd solution. It precipitated green powder. I read in some forums that I should filtrate the powder and wash it with cold water until it gets yellow pdDMG powder. When I washed it it got white color. Am I doing something wronge? Or I didnt make the DMG solution correctly. I tested the green solution with Stannous chloride before and after adding DMG solution. Before it was positive after adding it got negative with the green precipitate. What should I do?