Gimp
Remove color
- pick color with with the Color Picker ( key o)
- select fuzzy select (key u ) set threshold as 0
- click on the color to select
- press ctrl+x to remove
Replace color in image
- select original color with the Color Picker ( key o)
- select menu Colors, Map, Color Exchange
- Paste the RGB code HTML notation in the from color
- Write the target color RGB code HTML notation in the to color
- click OK