I'm plying two colourways into one yarn and I love the result.
Last summer I bought 9 braids of roving, 4 ounces each, of a lovely Merino/Silk/Kid Mohair blend dyed by Jude of
Ewesful Creations. She had six braids of the first colour but I wanted 9 in total so there would be no question of running out of yarn mid project. I found 3 more blue braids, but they were brighter. Another spinner voiced the opinion that the brighter skein would clash with the others but I took a chance and went ahead and purchased them anyway.
Turns out it was a good choice! I have spun up 2 of the darker braids and one of the brighter colour and then plied them together. I'm very happy with the resulting bright denim colour (most accurate colour representation is in the first picture, a hand wound 10.3 ounce ball of 3 ply).
I still have 2/3 of the roving to spin up --- another 6 braids. I had only gotten started on this lot last fall when our puppy, Teddy, arrived and he required all of my attention. I'm finding that I can spin again now that he is 8 months old --- as long as I keep the e-spinner and the roving up out of his reach. It's not always possible so this may take awhile!