How hard would this be to do?

[DeathByGuitar]

So I'm thinking of making a theme for the first time, but all I really want to do is change any instance of seafoam green in the UI (like the meters and icons) to orange like Default Analog does. Is this something that people usually do by hand, like opening each icon in Paint or whatever, or is there a way to batch process these icons for something this simple? I don't mind doing everything one-by-one but I figured I'd see if there was an easier way.

[Luster]

I started my mod with the same thoughts and ended up editing the images one by one. Part of the reason are the pinky lines which have to stay the way they are exactly regarding colour tone and brightness. Most batch processors have the basic capabilities to do job except ignoring those pink lines. For basic image management and some editing / converting I can highly recommend FastStone ImageViewer.
One advantage of the by hand solution is the raising lust for more. Meaning you get the hang for it step by step and soon you start writing Walter code.

[DeathByGuitar]

Makes sense. Thanks for the info!

[Judders]

I don't know about batch processing in GIMP, but in Photoshop you could record an action along the lines of colour selection (pink... magenta?) > invert selection > hue/saturation colourise. Then you can run that action using the batch processing feature.