Here is a link to Pearsall Color chart

http://store1.yimg.com/I/lewis-and-clark_1864_65338218

I have seen some soft-hackle flies tied with Primrose, and the effect
( to my eyes ) were that the very light yellow thread when wrapped over a bronze hook produced an almost pinkish-beige color in the body.
Similar to the color of the background on this FAOL page.
The tyer attested to the effectiveness of this color.