In GIMP, to change white to blue:

• Open the image file
• menu Colors/Map/Color Exchange
• Press the colour selection for "From Color". Set R, G and B to all 255. Press OK button.
• Press the colour selection for "To Color". Set R and G to all 0. Set B to 255. Press OK button.
• Press OK button.

White and black are special... If you want to translate all other colours then:

• Open the image file
• menu Colors/Hue-Saturation
• Press "Master" button
• Drag the Hue slider