What is the native color of a Dialogbox?

I’m building a form that will be called by a dialogbox, but whatever color I choose for the form, the pop-up dialog shows a small border in a different (grey) color on the right hand side and along the bottom. I would like the whole of the dialog box to be one color. Can I do this?

Subject: What is the native color of a Dialogbox?

Always use the color named “system”. You can find it on the color pallet, in the upper-right corner.