Are multicolor decks in any color combination viable in modern Magic?
Running 60 is still the best plan. You have the highest likelihood of drawing into your best cards when you have fewer cards.

As far as seeing more multi-color, right now we're in a multi-color block. Retrun to Ravnica (RTR)and Gatecrash (GTC) each feature five of the ten Ravnica guilds.

Right now in current standard are the ten 'shocklands', lands that come into play tap unless you pay two life and can tap for two colors (in RTR and GTC), for example Blood Crypt; a cycle in M13 of allied dual lands which come into play tapped unless you control a land type that it taps for, for example Glacial Fortress, and a cycle of enemy dual lands which do the same from Innistrad, for example Isolated Chapel.

Dual lands are the primary source of mana fixing. RTR and GTC also released gates, which are dual lands at common that always enter the battlefield tapped. These are typically considered too slow for standard constructed play.

Green is still considered the fixer color, granted access to tools like Caravan Vigil, Arbor Elf, Avacyn&#39;s Pilgrim, and Farseek, Mulch, Ranger&#39;s Path, Seek the Horizon, or if you have insane mana already like perhaps in a Commander game, Boundless Realms.

Currently Llanowar Elves and Birds of Paradise have rotated out of standard. They aren't usually out for long, so we stand a chance to see them in 2014, but honestly with all the fixing in right now, they aren't as necessary.

As to your question of "pretty much every combination of color is a viable tactic" you could make that argument. Each two color combination has a Ravnica guild, and half of the three color combinations have an Alara shard. Each of the Ravnica guilds is seemingly viable in standard, although many of them do have a third splash color. There are fewer monocolor top decks right now just because the set is so focused on multicolor decks.

Other formats have different archetypes. There is no single Commander deck that is winning everyone's hearts and minds. Jund (and to some extent, Storm) is completely dominating Modern to the extent that the DCI just banned two cards, one core to each deck, to level the playing field a little. Legacy and Vintage I don't follow enough to really comment on, but I'll say as far as I know there are no dominating color patterns there.