Fimbriation

In heraldry and vexillology, fimbriation is the placement of small stripes of contrasting colour around common charges or ordinaries, usually in order for them to stand out from the background, but often simply due to the designer's subjective aesthetic preferences, or for a more technical reason (in heraldry only) to avoid what would otherwise be a violation of the rule of tincture.

(In heraldry, "metal" refers to gold and silver, frequently represented using yellow and white respectively.

One example of this is the flag of the Faroe Islands, which separates a red cross from a white field with blue fimbriation.

The flag of Uzbekistan also uses this form of "pseudo-fimbriation" - it adds a thin red band between a colour and a metal, separating blue (above) and green (below) from a central white stripe.

The white fimbriation along the white part of the saltire - possibly unique in vexillology - is responsible for the famous "lopsidedness" of the Union Jack, giving it the appearance of having a red saltire fimbriated more widely on one side than the other.