Scale is an important consideration when choosing a scarf. A large scale tends to take over an outfit – so the scarf is featured at the expense of the other outfit components. A scarf with a very small scale pattern adds a subtle accent to an outfit and ties together closely related colors; a tiny pattern looks like a texture and doesn't invite close inspection.
A midscale pattern is often the best choice. A midscale pattern is small enough to complement the face and large enough to be comprehensible to those interacting personally with the scarf wearer. The observant conversationalist (or silent admirer) could identify the scarf as floral or nautical or word based without violating socially conventional proxemics. The wearer of midscale patterned scarves invites interaction but not intimacy and establishes a presence without dominating the scene. After all, we don't want others to put on their reading glasses to see the pattern on the scarf!
The colors of an excellent quality scarf will be vibrant and consistent. If all colors are in the same family they should enhance one another, not compete. If there is an accent color it should be balanced and integrated.