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I have a title card with black type alongside a green icon on top a white background. I would like to reverse them so that the black type becomes white, keeping the green icon, against a now black background.

Is there a way to do this?

As always... multiple ways to do this.
all involve at least a couple of steps...
First
in the bottom left "Background" menu in the layer panel you can change the background to black.

Then the text,
you can change its color from black to white in different ways.
But first you need to isolate the text from the green icon by making a selection.
then you can either:

- apply the fxstack with the 'Stylize> 'Negative' effect
or
- lock the layer's alpha channel (activate the black bullet point under the ALPHA symbol, on the left in the layerpanel and for the layer on which your text sits)
and paint the entire frame white, by using 'filled rectangle' tool or even simply by applying a large penbrush

Got it! Thank you Peter!