For multicolor, I like poison spray for wither and poison, which now is useful given the larger hp/resistance pools.
But for consistency, I just tried out and really liked dual firewalkers rings on a barb with red spells. Enough red gets on the board to make sure you fill spells fairly easily.
I would say the current focus of PVP is physical power and the weapon you equip.
While I did favour a 4 colour spell combo in 0.35, the spell changes in 0.36 - increasing the cost of most spells as well as reducing the amount of mana earned from matching gems - has made being able to reliably cast multiple spells in the 2nd or 3rd round much harder.
Physical attacks on the other hand got a massive boost in strength linked to rarity and level, so if you got the L35 Runic Mace from the update, or have something even higher level, that will reliably out damage any spells in the first couple of rounds of the battle.
The other major change from 0.36 was boosting equipment stats so armour and resistance are boosted a lot more with higher level items. But this is where it starts to promote odd behaviour in PVP as opposed to PVE.
To score well in PVP and get a high place on the leaderboard you want to be regularly scoring 2,450 or 2,475 in battles, which means killing the enemy after 1 or 2 moves without taking damage. If you equip your best gear the game matches you against an opponent with similar gear score, which if that results in your opponent having 5/6/7k combined armour and health means you aren’t going to kill them in a couple of rounds even with the best luck.
So it promotes fighting like Conan the barbarian - strip down to minimal gear and take your biggest weapon with you. Lower gear score matches you against lower armour/health opponents, while your primary damage output (physical weapon) is largely unaffected.
This is the biggest piece of advice I got from this post. Lower gear score for lower enemy defense!
As long as they are not outfitted the same but swinging a big meat stick. A legandary weapon only counts 150 towards gear score! 
I sure do love finding the Conans in my PVP brackets each week! Makes PVP extremely tedious