[NTG-context] Change color of EPS file.

Hello, I have a EPS file wich contains black lines and no background. The background of my presentation is colored, so I would like to put this figure in white. I tried a \startcolor … \stopcolor environement without succed. Is there a way to do so? In last resort I can put a white background with: \placefigure[left,none]{caption}{\externalfigure[demo-b][background=color,backgroundcolor=white]} Best regards