There's a couple of techniques that I love to use to really make the most of high-contrast variegated yarns. These are the ones that if you to take a grey scale photograph of the skein, it's noticeably varied in grey tones and pale or white.
USING A TEXTURED SOLID COLOUR YARN FOR A MARLED EFFECT
The top photo is a fingering weight colourway we dyed a few years ago and I stashed a skein or two. It's a speckled yarn on an undyed base so high-contrast. I've used Fyberspates Cumulus, a fluffy baby alpaca and mulberry silk laceweight, to hold done on this project, a simple square crochet cushion cover. Not only does it appeal to my tactile need for fluff, it brings cohesiveness to the dye style and is a technique that works both on crochet and knitting.
USING A SOLID COLOUR YARN IN SIMPLE COLOURWORK
This is another of my favourite tricks to tame your wildly variegated yarn. In my example here I've used a hand-dyed semi-solid yarn but like with the fluffy cushion above, there's absolutely no reason why you can't used a mill-dyed yarn. Not only are they just as beautiful as hand-dyed yarns, they're priced more competitively due to much higher production numbers so can be a great way to supplement a beloved skein of hand-dyed yarn.
These photos show the pattern Yarn Tamer by Louise Zass Bangham from the book 'Knit Play Colour' (Love Crafts link) which is a cowl that looks far more complicated than it is to knit. It's moss stitch with the two colourways arranged in a way that creates this incredible effect.
The speckled yarn is This Ain't A Scene and the semi-solid blue is Persia, both repeatable colourways. This yarn base is Tia Merino, a superwash fingering weight single-ply merino which is perfect for accessories like this.
LOOK UP YARNS
Fyberspates Cumulus- we stock all the colours
Tia Merino- hand dyed by us