Currently, if you were a guild tabards appear white in Cyrodiil if the guild was made on a faction different than the character you are wearing the tabard on. I don't understand why this is the case. You should be able to wear your guild tabard in Cyrodiil no matter what faction you are (multi faction guilds). And the worst part is you can't change your guild's faction without re-creating it.
Fire Cloak - VR12 DK - Nord - EP
Ámeer - VR15 Templar - Imperial - AD
The Mágician - VR16 Templar - Imperial DC
Magíc - VR16 DK - Dark Elf - DC
Àmeer - VR16 Templar - High Elf - DC
ámeer - VR16 Templar - High Elf - AD
Æ ámeer - VR16 Templar - High Elf - EP
Ameer Flow - Level 34 Nightblade - High Elf - EP
Youtube:
https://youtube.com/channel/UCFNmXCgmTVo-T-p1BIVLxbQ