For me it’s definately the colour, as strange as it seems.
Take the following example:
I have less than zero interest in the blue/gold and grey/gold Anglams pictured here. Even if someone offered me one for half price I wouldn’t be interested… I find the colour combinations a tad offensive to my eyes.
On the flipside, when I saw the silver w/red rings version, I actively searched around till I could find one and then bought it straight away, even though I previously hadn’t given much thought to the Anglam CC as a yoyo I would want.
So to me it’s all about colour. There are many throws out at the moment that have a shape and specs that I’m interested in, but I haven’t bought yet because I’m not drawn in by any of the current colourways (Space Cowboy, Aviator, Cyborg, Berserker CC, Laser just to name a few). :-X
After colour, I’d probably say that design was the next big thing for me. It takes a very special colourway to make me buy a yoyo that I really don’t like the design of, whereas on the flipside if I see a yoyo that has a very interesting design to me (Tropic Spins Shipwreck for instance), I may allow a bit more wiggle room for specific colourways.