Yep - dark for dark, light for light. What my SA said, in any case!
Want to know an interesting scarf anecdote? Hermes were intrigued to find that some of the scarves were getting a very fine white mark in the corners of the new scarves that had just returned from the ladies who sew the hems. After much research, they discovered the fine white marks in the corners of the scarves was SALT from the saliva of the ladies who roll the hems. To ensure the roll is tight and uniform, the 'roulotessess" (sp?) lick and spit on their fingers and roll the silk tight between their fingers before stitching. When their saliva dried, salt formed in the corners of some of the darker coloured scarves.
Have a look at your newer (unlaundered) scarves and see if you have traces of salt!