I don't know what a bicolor is. Do amoenas count?
World Premier is a shocking iris with big blooms. It grew great for me.
Renee

How about Supreme Sultan? Tried and true, huge flower, knocks your socks off.

Well, what blooms well in my garden may not behave the same in a different zone. these are the two toned in my garden that are my favorites, not all are huge flowers though.
How about Dangerous Mood, this year the fall were't as dark as usual,normally they are almost black. Phantom Masquerade is similar, maybe more dramatic

Dawn to Dusk is really pretty, doesn't seem to be multiplying very well here, not huge blooms either, but so striking

Jurassic Park & Edith Wolford look similar, but I like the slightly softer tones of Edith better. Jurassic may multiply better here. Right now I can't remember how large the blooms are. Jurassic may be bigger than Edith. This is Edith

Fashion Queen, fairly large blooms, striking though

Enchanted one is bright, not huge blooms though

Florentine Silk, 1st year here but it had large blooms & bloomed well.
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Backdraft, med blooms but great multiplier & bloomer

Thinking out Loud, later bloomer & does well here, large blooms

Vigilante, I think very dramatic & bloomed well

Did you mean just ones that have two different colors between the standards and the falls? I have had Edith Wolford, and recently purchased World Premier which was blooming its heart out in a pot, so it must like to bloom. It took Edith a year to get going, but she is beautiful. An older one that was really bloomy and grew well for me is Spiced Custard. That is the one you can just see in the upper right of the picture below.

Wow! Great pics. Thanks for all the suggestions.

Wow, great photo of Edith. You should submit this to the AIS photo contest.
Renee

One that jumps to the front of my mind from this season is 'Peking Summer'. Big blooms, vibrant and eye-catching, good performer. Bright yellow-gold standards and glowing red-maroon falls with a thin orange-copper rim.