by Peter J. Sloetjes, MSc. (Developer) on Sept. 27, 2016 · permalink

Just click 'Invert lightness', then click 'Scale to lower lightness' once or twice, and then click the 'star' or 'plus' button for saving, and you'll have a light-gray-on-black theme (on most pages).

You may also start from theme 31 and then click one of the 'Shift hue' buttons repeatedly to obtain a gray-on-black theme which retains some of the saturation of e.g. links with the hue you like most.

With Color Transform, you can save only one custom theme. Try Colorific if you would like to save more custom themes or would prefer more extensive customization.