I am trying to change the background on the widgets so they are completely transparent like the Desktop Plasmoid. In the image you can see that unit converter's background is different. I'd like to make it more transparent like the Desktop plasmoid background.

That's dependent on the plasma-theme in use. You can mix-and-match themes using the desktop theme details settings (under advanced user settings) though. Of course, by doing that one of the widgets won't look like air anymore but may be worth a shot.

I'm not sure which one you need to change to get it more transparant, but make sure to have a couple of themes installed (bare naked and glassified are good candidates for transparancy) and play around with "widget background", "translucent background", and "dialog background". Maybe even "panel background".

Thanks. Changing the widget background to Glassified theme did the trick.

Plasma::Applet:: setBackgroundHints(const BackgroundHints hints); with NoBackground

dridk wrote:Plasma::Applet:: setBackgroundHints(const BackgroundHints hints); with NoBackground

Thanks. I assume that is code I would need to change for the theme. I'm new to Linux so am very green when it comes to how it all works.

Using a custom background is a really bad idea. According to Plasma UI specifications widgets shouldn't use a custom background but they should use a standard one. Anyway If you need something transparent you should use TranslucentBackground as background hint.

That's why I suggest to add a background hint selector in each Plasma Configuration dialog..
But I think the policy of plasma is : All same background for all plasmoid.