Purple + Yellow-Green

There's got to be a way to do this.

I've been interested in weaving in two or more colors, but when the pieces are finished, they look a third color. This one, as you can see, is in purple cashmere/silk warp (i.e. a little bit of sheen) and blue-y-yellow-green cashmere (matt) weft. When I hold it up and wave it or shake it like this, the whole piece looks a bit more... silver-y. Can you tell me what I do to capture that color? I'm doing a whole lot of these with shiny cottons, too. Intriguing stuff; I'm sure there's a name to this... occurrence/symptom(?), too. Any help appreciated.