Square yellow color when #FFFFFF but working when #ffffff

[geeky3]

When i type "#FFFFFF" it gives me annoying yellow box but if I type "#ffffff" than it works perfectly, also uppercase with any other color works, I have issue only with '#FFFFFF". Any idea what is causing this ??

[TeralGoe]

Yep, I noticed that, too. Looks like this is happening because GutterColor have #ffffff.png in the cache folder and cannot create a new file with same name.

However, you can recreate all files through clearing cache:
Command Palette -> GutterColor: Clear Cache

[marandac]

Applied a quickfix to this problem by forcing lowercase on the color strings in the line.py code (in Win10, \User\Your Username\AppData\Roaming\Sublime Text 3\Packages\Gutter Color).

Changed those instances:

if matches:
        return matches.group(0)

to

if matches:
        lowercase = matches.group(0)
        lowercase = lowercase.lower()
        return lowercase

Once you update the file and clear your cache as described by @TeralGoe , the problem should be gone.

As reference, I attached the modified line.py file
linepy.zip