Colored O Rings?

[George Saad]

I have a few carto tanks and was thinking if I can swap the boring black o rings it will not only look good but I can match/mark different juices by its o ring color! Where can I find those?

 

[Elantis]

I don't know if these are the type of tanks you have but IBTanked sells colored O-rings for their tanks:

http://https://www.ibtanked.com/accessories/o-rings-and-washers/o-rings-by-device/19mm-color-pack-1-o-rings-detail

These are for the 19mm tanks.