fimbriation

In heraldry and vexillology, fimbriation refers to small strips of colour (technically called "tincture" in this sense in heraldry) placed around common charges or ordinaries, usually in order for them to stand out from the background, but perhaps just because the designer felt it looked better, or for a more technical reason (in heraldry only) to avoid what would otherwise be a violation of the rule of tincture.
Take, for example, this
.