Monk's Perspective Shift's requirement of two different Favor that aren't of a PC's Color seems difficult to achieve for dual-colored characters, especially those without Black as one of the two. Prowess alleviates this somewhat but since you only get two Stances a player might be at the mercy of a GM giving out different colored Favor as a reward.
For example, I built a Green/Blue Monk. Unless I also choose both Sun and Boulder Stances there is no direct way to meet the requirement of "2 different Favor of any color other than your own".
Maybe there could be more ingrained ways of attaining other colors of Favor, or more explicit GM guidelines about what colors of Favor to award
Monk was always a bit of a strange Class to design. The intention behind Perspective Shift was to create an incentive for the Monk to try and get Favor from other PCs via Offers (When you X and they accept, they gain Y) and the ability to get different colors from Prowess was sort of an extra bit of help that made it possible to do without outside help. You're probably right that it might need a bit of an update to make it more doable, but the automatic success you can get is (I think) a pretty good reward for the extra hoops to jump through. Thanks for the feedback!