The Colorize tool renders the active layer or selection into a greyscale image seen through a colored glass.
The slider and the input box allows you to select a hue in the HSV color circle (0 - 360).
The slider and the input box allows you to select a saturation: 0 through 100.
The slider and the input box allows you to select a value (luminosity): 0 through 100.
The Preview button makes all changes dynamically so that they can be viewed immediately.