The status indicators on file tab are small images in resources of UltraEdit. So it is not possible to customize the colors.
It is possible to open Advanced - Settings/Configuration - Application layout - File tabs - Miscellaneous and uncheck the setting Display status icons. Then a file with not saved modifications is indicated with * (asterisk) after file name on its file tab.
Best regards from an UC/UE/UES for Windows user from Austria
For me the 'modified' indicator is not only red, it's a diamond shape. The 'saved' indicator is a green circle (a never modified file has no indicator at all). So even without color these states can be distinguished.
If the diamond vs. circle isn't distinctive enough of a difference, perhaps IDM can be emailed to suggest that they make the shapes even easier to tell apart.
I see that the help file shows that the 'modified' indicator is supposed to be a yellow circle, so maybe different versions of UE use different images? I'm looking at UEStudio 16.10.0.1 at the moment (which uses a diamond shape for modified files).
I have reported already on January 2016 that the symbol for Local modified file (unsaved) in help is not correct anymore since several versions of UE/UES because it is a red diamond instead of a yellow dot. I have reported this small help issue once more on August 2016 this time with attaching even the PNG file to replace in CHM file. But it was again forgotten by IDM to replace the image in help as I could see on viewing the help page with UE v24.00.0.76 and UES v17.00.0.18. Therefore I have reported this help issue once again today.
I can imagine that the small dark red diamond with a dark scheme like Slate is hard to distinguish from green dot. I have disabled the display of the status as well because I favor a puristic user interface and prefer the asterisk appended on file name.
Best regards from an UC/UE/UES for Windows user from Austria