In this GIMP tutorial you will see how to make the color of text alternate between light or dark depending on the background. I developed this procedure to meet the needs of someone who follows this blog and made a request for help. I hope others among you will find it useful, too.
Open the background image.
Duplicate the background layer, Layer- Duplicate Layer. Desaturate the background layer copy, Colors - Desaturate... by Luminosity.
Apply the threshold filter to the background layer copy, Colors - Threshold…, push the slider to the right until there's hardly any white bits in the black.
With the Brush Tool, paint out any details to match the dominant color, black or white.
With the Text Tool create your text layer in black or whatever dark color you want to use. Position it with the Move Tool. Expand the text layer to the image size, Layer - Layer to Image Size.
Make the text layer invisible by clicking the 'eye' icon in the Layers pallet.
Make the black and white layer active by clicking it in the Layers pallet. With the Select by Color Tool in Replace the current selection mode, click anywhere in the black.
Make the text layer visible and active. With the Select by Color Tool in Intersect with the current selection mode, click anywhere in the text. You should now have the portion of text that overlays the darker buildings selected. Make the black and white layer invisible.
Create a new transparent layer, Layer - New Layer..., on top of all the others and name it Light Text. Now, fill the selection on the Light Text layer with white or whatever light color you choose, Edit - Fill with BG Color. Deselect, Select - None.