I'm spitting I just posted this! It got lost.
Again: I feel that colour variations hide stitch patterns, including cables. You should Google to look at variegated cables, etc., and see whether you feel the same way or not.
If the colour changes are done so that you get a few inches of one colour, then a few inches of another, the pattern will be less obscured. I think Noro Kureyon changes in this way, Google it for some pictures if you're not sure what I mean. Wools with many colours mixed together and tiny repeats are more likely to lose the pattern. It may be helpful to look for a knitted example to show you how the colours change - at the shop, or online. Remember that if the swatch is wide, the colour repeats will appear to be shorter than what you'd get in a scarf.
If the 'variegation' is in fact only tiny flecks of different colours it may
not hide the cable, some people like the 'tweedy' effect this gives.
And if you like the wool, and intend to continue knitting, maybe you ought to buy it anyway - I'm sure you'll find a pattern for which it's perfect!