Hello! Violet is a dropdown option in Surf Ice, but not in MRIcroGL. I was going to copy the color from the Surf Ice lut folder and paste it into the MRIcroGL lut folder, but I can't find it. When I try to use the Color Editor in MRIcroGL, I end up accidentally changing the color of the underlying template brain rather than the overlay. Any advice on how to use this color for overlays in both software packages?

You can always create your own custom color lookup tables. Just place a text file with the extension .clut in MRIcroGL's /Resources/lut folder (for MacOS users, right-click on the MRIcroGL and select "show package contents" to see these folders). Since Violet is red+blue, here is a simple violet color scheme that goes from black (RGB = 0,0,0) to violet (RGB = 255, 0, 255). Name this "Violet.clut" and place it in your out folder:

[FLT]
min=0
max=0
[INT]
numnodes=3
[BYT]
nodeintensity0=0
nodeintensity1=128
nodeintensity2=255
[RGBA255]
nodergba0=0|0|0|0
nodergba1=128|0|128|64
nodergba2=255|0|255|128

Thanks for your suggestion! I've created the "Violet.clut" file in the lut folder, but I don't see it the color as selectable in the software. I've restarted the software as well as my computer. Is there something I need to do in order to point the software at the new .clut file?

I can not replicate your problem.
 1. Try renaming one of the other files in your out folder (e.g. "actc.clut" -> "new name.clut"). After changing the name, restart MRIcroGL. If this does not fix your problem, perhaps you are running a different copy of MRIcroGL than the one you modified.
 2. What is the version of MRIcroGL and the operating system? The "About" menu item should provide all you need to know. One thought is that the most recent releases of macOS require application notarization that signs all the files associated with a program. In this case, it may be hard to make modifications, This would be a limitation of your operating system, not my software. You may be able to change application permissions in the Preferences window, or by launching the program from the command line, e.g. "/Applications/MRIcroGL.app/Contents/MacOS/MRIcroGL". One of the challenges with developing for macOS is that locally compiled executables are trusted in a way that downloaded ones are not, and this makes it hard for developers to mimic how users experience a tool.

Problem solved! I uninstalled then reinstalled the program. Thank you very much for your help!