Gimp: Change a signature color from black to blue, preserving the tones

Question

I have a scanned signature written in black pen. I have removed the white paper parts of the image using alpha transparency.

After using it several times, it seems that it would look better if the color of the signature is blue rather than black.

How can I change the color of the signature from black to blue, while preserving the different color tones and shades (i.e. Black becomes dark blue, light gray becomes light blue)?

Answer 1

• Set the foreground color to dark blue (the color that will replace black), the background color to white.
• Set the image to RGB mode if not already such: Image>Mode>RGB
• Set the current gradient to FG to BG (RGB) (fourth from top in Gradients list)
• Colors>Map>Gradient map

Answer 2

From the top menu, choose:

Colors -> Colorize

As you pick the color on the palette, it will instantly apply to your image and you can quickly re-iterate to achieve desired result. It's super smooth, all gradients are preserved. Very realistic outcome.