Assuming both of these are turned on in Preferences / Favorites and Recent / Labels:
- Enable label storage in the file system (NTFS volumes only)
- Automatically store labels in the file system if possible
Also assuming the drives in question are NTFS (or another filesystem that supports Alternate Data Streams).
Making custom labels work across multiple machines/users requires copying/merging the config files that store the label definitions between machines/users. Each label has a unique internal ID which is what is written into the filesystem. The label's name is only for display (otherwise the label would break if you decided to edit the name).
So if you independently create two labels named "Cat" on two machines, they won't be the same thing. Could that be what's happening?
You can find the label definitions in this file:
/dopusdata\ConfigFiles\colorgroups.oxc
For example, here is mine:
<?xml version="1.0" encoding="UTF-8"?>
<colorgroups>
<categories>
<category display="Colors" name="colors" />
<category display="Status" name="status" />
<category display="Backgrounds" name="{50A05DC8-17BC-4D0F-9E09-5EC59DFA66A9}" />
</categories>
<groups donedef="2">
<group bg="none" category="colors" fg="#0000ff" flags="0" icon="none" id="{A3B60A15-3008-40C5-B96B-615CF0005B25}" name="Blue" sel_bg="none" sel_fg="none" />
<group bg="none" fg="none" flags="0x801" icon="none" id="{FAD2929D-4C83-4162-965A-ADF23300A701}" name="Bold" sel_bg="none" sel_fg="none" />
<group bg="none" category="status" fg="none" flags="0" icon="none" id="{5342DBF5-EABE-4B8B-B6AD-584AE87CF76C}" name="Cat" sel_bg="none" sel_fg="none" status_icon="E:\Temp\Video Opus 12.10\Pictures\Chester.png,0" />
<group bg="none" category="status" fg="none" flags="0" icon="none" id="{C866FA3D-5199-49B9-9B68-68436795DC9B}" name="Checked" sel_bg="none" sel_fg="none" status_icon="/home/dopus.exe,31" />
<group bg="none" category="status" fg="none" flags="0" icon="none" id="{71B3907E-3F17-401A-83BE-F4F6D5848656}" name="Complete" sel_bg="none" sel_fg="none" status_icon="/system/imageres.dll,226" />
<group bg="none" category="Colors" fg="#3399ff" flags="0" icon="none" id="{F8155445-2799-4FE0-8113-04EF8F38010E}" name="Cornflower Blue" sel_bg="none" sel_fg="none" />
<group bg="none" category="status" fg="none" flags="0" icon="none" id="{04C7CEE6-F91F-49A4-A007-3E7BC82B06FE}" name="Flagged" sel_bg="none" sel_fg="none" status_icon="/home/dopus.exe,32" />
<group bg="none" category="colors" fg="#139b36" flags="0" icon="none" id="{DEA7AD56-705E-46E7-96EB-66FC16625A1C}" name="Green" sel_bg="none" sel_fg="none" />
<group bg="#ffff00" category="{50A05DC8-17BC-4D0F-9E09-5EC59DFA66A9}" fg="#000000" flags="0" icon="none" id="{615AD2AE-9DFF-4C38-B29B-BE74D127E5F2}" name="Highlight" sel_bg="none" sel_fg="none" />
<group bg="none" category="status" fg="none" flags="0" icon="none" id="{284E4FD5-DFCE-4403-95A9-52A86E827927}" name="Important" sel_bg="none" sel_fg="none" status_icon="/home/dopus.exe,30" />
<group bg="none" category="colors" fg="#ff8000" flags="0" icon="none" id="{FEDC8A0B-6F3B-4113-A733-17A008C87ADB}" name="Orange" sel_bg="none" sel_fg="none" />
<group bg="none" fg="none" flags="0x18003" icon="none" id="{11B10506-6D96-4287-90B0-FFE620B67DE4}" name="Pinned" sel_bg="none" sel_fg="none" />
<group bg="none" category="colors" fg="#8000ff" flags="0" icon="none" id="{53B6C3BF-C513-4E2D-BE6C-71F6C7177492}" name="Purple" sel_bg="none" sel_fg="none" />
<group bg="none" category="colors" fg="#da2929" flags="0" icon="none" id="{2F499E2B-8B6E-4B80-8E3B-C73E032E801F}" name="Red" sel_bg="none" sel_fg="none" />
<group bg="#f3c0c0" category="{50A05DC8-17BC-4D0F-9E09-5EC59DFA66A9}" fg="#000000" flags="0" icon="none" id="{D16485A5-F89E-43E1-AC65-71AA2B56624D}" name="Red Background" sel_bg="none" sel_fg="none" />
<group bg="#96ce71" category="{50A05DC8-17BC-4D0F-9E09-5EC59DFA66A9}" fg="#000000" flags="0" icon="none" id="{C2C0C936-123E-4316-A005-391E026724BF}" name="Row Even" sel_bg="none" sel_fg="none" />
<group bg="#f0e2a2" category="{50A05DC8-17BC-4D0F-9E09-5EC59DFA66A9}" fg="#000000" flags="0" icon="none" id="{C44E52E0-E92F-40D1-A281-B481D6437094}" name="Row Odd" sel_bg="none" sel_fg="none" />
</groups>
</colorgroups>
Taking this line as an example:
<group bg="none" category="status" fg="none" flags="0" icon="none" id="{5342DBF5-EABE-4B8B-B6AD-584AE87CF76C}" name="Cat" sel_bg="none" sel_fg="none" status_icon="E:\Temp\Video Opus 12.10\Pictures\Chester.png,0" />
You can see it's using E:\Temp\Video Opus 12.10\Pictures\Chester.png as its icon, and that works as long as that file icon exists on all machines (e.g. if E:\ was a mapped network drive, or had a local copy of the same folder.)
The label's name is Cat but that name is just what's displayed in the UI. The internal ID is {5342DBF5-EABE-4B8B-B6AD-584AE87CF76C} and that's the important part for making it work for multiple machines/users.
(As an aside, please link your account.)