The GR Ramp decks have been making waves over the past few weeks in Standard events. The idea is to play a few ramp spells and top the curve off with Ugin, the Spirit Dragon or Ulamog, the Ceaseless Hunger. Being able to chain Ulamogs with Sanctum of Ugin made the control matchup favorable, and resolving a single Ugin is often enough to singlehandedly defeat midrange decks. Aggressive strategies are a problem as lots of damage can sneak in before the ramp deck even sets up.
For this deck, splashing red was almost free. Access to both Wooded Foothills and Cinder Glade alongside a single Mountain that many of the ramp spells could naturally fetch out made the splash close to painless. It was also necessary as sideboard sweepers like Seismic Rupture were some of the few ways to try to compete with the aggressive red strategies. The problem is that aggressive creatures with toughness greater than 2 can be a real problem. We are living in a world of Mantis Riders and Anafenza, the Foremosts which come down early and hit hard. The ramp deck risks dying before Ugin can clean up the mess.
Deciding to pair the ramp deck with black instead comes at a high cost. The mana is worse. That being said, access to Languish is a potentially huge gain. After sideboard, cards like Duress (which honestly could be main-decked right now) and Transgress the Mind help force through important threats, while stripping opponents of their answers —or threats, when necessary. Another early interaction spell in Ultimate Price can buy the ramp deck the time it needs to set up an unbeatable late game.