How to change a single colour in an image when converting to a png?

Goal: convert an icon (single-colour, black, with transparent background) from either an svg or xcf, to a png and change the colour of the icon (e.g. black becomes white or a specified hex colour).

ImageMagick version: 7.0.11-6

Progress so far: I have a Windows batch file that

for each xcf (Gimp) file in the folder will
- for each file col-*.* in the folder
  - resize, resample and then remap against the col-*.* file and save the png

I have had some success, but have found that

the col- files can't be all one colour (the colour I want) otherwise the whole new png is just that block colour too.
if the col- files are pngs with the colour I want and a transparent background it works with dark colours, but lighter colours end up fuzzy around the edges.
-remap does not work with svg source files and using -fill and a hex value gets a fuzziness on all png images created.

Is there a better way to re-colour these pngs? Or a way to stop the fuzziness? I have just started working with ImageMagick. Many thanks!

Current batch file

@echo off

set resolution=72
set width=48

setlocal enableDelayedExpansion

for %%i in (*.xcf) do (
    echo Converting [ %%i --^> %%~ni.png ] ^(%width%@%resolution%^)
    
    for %%x in (os-col-*.*) do (        
        magick %%i -resize %width% -resample %resolution% -remap %%x %%~ni-%width%-%%x.png
        echo Done %%i - %%x
    )
    
    echo Done %%i
)

black png, no fuzziness

fuzziness in a png with -remap applied

Solution

Using ImageMagick, if your input is a single color and you want to change it to another while retaining the transparency, this command should do exactly that...

convert input.png -fill #75965b -colorize 100 result.png

That creates this output image....

That is in IMv6 syntax. For IMv7 use "magick" instead of "convert".