Players will not be forced to engage with the shades of gray (murder hobos will murder hobo).  But it will be a theme that pops up frequently if the players are looking for it.  A few of the shades only really work if players know creature alignments.  Like "why is the chaotic good copper dragon helping the BBEG?"  OR "Ok... so why exactly is a LICH super focused on bettering the lives of the common folk, while also protecting the delicate balance of life and death on this plane of existence?"

Remember, passive checks are a thing. If I had new players that were just completely missing my hints left and right and at least one of them had decent wisdom or Insight training, I'd tell them bluntly that their character noticed something wasn't right with their passive Insight.

Passive Investigation would work too. Even if the players are dumb as rocks (kidding obviously, being unfamiliar with the game doesn't equate to dumb), the characters are competent. They would notice.

Gets an entire party of warriors and barbarians (and a melee bard for healing).

I'm coming off of 6 months of running Shades of Grey gaming.  It has problems.

The biggest thing I've learned is that a SoG campaign leaves the players with very few clear victories and I have vastly underestimated the toll that will take on my players.  Everytime they turn around they're confronted with another "pick the least bad of these options" and that leaves them with a sense of "we won.... yay?" at the end of a story arc.  The first time it was fun; they saved a town, ended the rigged lottery but left it where the only way the people could survive was annual ritual sacrifice.  But they did position it so the town would return to volunteers.  There were no other real options in the Lore to do much better.

And even now they're in massive sprawling port town with no real unifying leadership, and their choices are to out the Harbor master (acting mayor) for his human trafficking (he's shipping victims off to Strahd) and risk out and out war in the streets again between all of the gangs that run the town.  Again, they don't have a lot of "good" options to consider and that's leaving them "why does everything suck?"  

So, my personal lesson in al this:  Players usually want to "win".  So if you're planning a "are we the baddies?" moment, give them a chance, immediately to set it right and to do so in glorious fashion.  Let them have a moment to say "we are going to fight the real evil here and bring .... it.. TO.. JUSTICE!!!!"