Today I did a little research on Gatherer to find which colors in the current Besieged/Scars/Scars look the best. For this analysis I only looked at commons and uncommons given you aren't going to see many rares or mythics beyond the first pick.
I find the two most important things in limited to be:
1. Creatures - Preferably ones that are bigger that your opponents creatures.
2. Removal Spells - Preferably ones that kill big creatures.
Now there are certainly differing opinions on other things that matter, such as card advantage creating card and evasion creatures with flying as strategies but I am trying to keep it pretty simple for this analysis and just see which colors are going to get you there by killing your opponents creatures and then beating them with big dumb fat guys. If your creatures are big enough then you can gain card advantage with profitable blocking and forcing them to chump block, and you don't need evasion if you kill all their dudes first.
First lets take a look at removal. Specifically creature removal, which in this format also includes artifact removal given the large amount of artifact creatures. Here is the breakdown by color and rarity.
Red: 3 (Arc Trail, Oxidda Scrapmelter, Into the Core)
White: 3 (Leonin Relic-Warder, Choking Fumes, Dispense Justice)
Blue: 2 (Volition Reins, Corrupted Conscience)
Black: 3 (Skinrender, Go for the Throat, Flesh Allergy)
Green: 2 (Virridian Corrupter, Slice in Twain)
Red: 5 (Burn The impure, Galvanic Blast, Shatter, Blisterstick Shaman, Turn to Slag)
White: 2 (Divine Offering, Revoke Existence, Arrest)
Blue: 4 (Bonds of Quicksilver, Quicksilver Geyser, Disperse, Steel Sabotage)
Black: 5 (Instill Infection, Grasp of Darkness, Spread the Sickness, Fumespitter, Virulent Wound)
Green: 2 (Silvok Replica, Pistus Strike)
Looking at these numbers, clearly Red and Black and the greatest quantity of removal spells, as well as the most effective ones. Most of the white and green removal will only target artifacts and most of blue will only return to hand. Clearly if you are employing the strategy I outlined above, it isn't going to work without playing at least one of these two colors, red and black. Now lets move on to the big creatures side of things.
I analyzed the creatures in the format by sorting them by casting cost and then looking at their power and toughness. In general in the format 1/1 is average for a 1 casting cost dude, 2/1 or 1/2 is pretty standard for a 2-drop, 2/2 is standard fare for 3, 3/3 is the normal for 4, and 4/3 or 3/4 is pretty standard for 5. Lets see what colors give us creatures above and beyond these averages.
As far as one drops go, you don't really want to play any of them aside from the occasional fume spitter, but if you must, Azuri's Archers is the biggest guy here and it is a 1/2 for 1 green.
At 2 mana 2/2 is the best you will find on a guy. Green gives you carapace forger, red has Goblin Wardriver, and white has several, Leonin Skyhunter, Leonin Relic-Warder, and Auriok Edgewright. Other honorable mentions are the 1/4 blu Plated seastrider and the 3/1 white accorder paladin. Take note that 2 out of the 4 white cards in this slot are uncommon so you won't be seeing a ton of them.
In the 3 mana the biggest creature is the Black 3/3 flying Necrogen Scudder which is pretty sweet. The only other creatures that seem to be above the curve here are Koth's Courier, a red 2/3, and Glissa's Courier a green 2/3. These two cards usually go super later even though they pretty much can battle with every 1,2, or 3 drop and some 4 drops without dying which is pretty sweet. White has a couple honorable mentions here with some good blockers in the 1/4 priests of Norn, and the 1/5 Loxodon Wayfarer.
For 4 mana, the only two creatures I would call ahead of the curve would be the green 3/4 Tangle Mantis, and the Red 4/3 Ogre Resister, Both of which you can usually pick up pretty late. Even 3/3's for 4 in the current format are not super common, with red having 2, black and white each having one, and several colorless. If you can find a Dross Ripper or a Peace/Pierce Strider you can probably fill out this slot with some good playables no matter what color you are. green also has the venerable 2/4 infect blightwidow.
5 mana will get you Kuldotha Ringleader, red 4/4, Melira's Keepers, green 4/4, and bellowing tanglewurm, another green 4/4. There are also a couple 3/3 flyers here with the white razor hippogriff and the blue sky eel school. the red 5/3 molderbeast is also a consideration here for a big dude.
At 6 mana Alpha Tyrannex is king at 6/5. Green also gives you the very sweet Fangren marauder at 5/5 with an excellent lifegain ability. The red 5/4 Flameborn Hellion is another big dude in this slot.
Notice a pattern? Green green green, which is not super surprising given green is all about big dumb creatures. There are also a pretty good number of good red creatures as well. White has a few good defensive creatures at the low end and black and blue are pretty outclassed here.
I would say that if you see the cards coming your way, there is no reason not to play red/green. It is going to be sweet, even without any bomb rares. Also if you pick up a veridian emissary and a horizon spellbomb you can throw in a swamp and splash for a instill infection, spread the sickness, or go for the throat. Next time I draft I will try out this strategy and I will tell you how it goes.