You would think that just a few colors would go well together and be very classy and satsifying (purple, lavender, white, or blue, white, or shades of berry and pink and so on), but I vaguely remember reading something (years ago) by the late great garden writer Henry Mitchell. He was an avid lover of irises, and his favorite colors (iirc) were the dark purples and blues (though of course he must have had other colors in there). He had some Grand Dame of Irises come visit his garden, and (again, iirc) a discussion ensued as to why the colors weren't satisfying. She told him something along the lines that he had to add this-or-those color(s) (I think a straw yellow might have been one of them) in order to make things pop. Mr. Mitchell didn't like the idea (over his dead body, and so on), but he did as she suggested, and next spring the entire iris garden came alive.
Right now my irises are either on their own, or are grouped (those in the ground, that is) with limited colors... purple, lavender, white, pink, or blue, white, yellow... I fear that these grouped irises aren't going to be entirely satisfactory, color-wise... but you have to start somewhere.