The Flying Circus was from a time when aircraft were still in their infancy and nobody was the sole authority of anything, and those that were were usually killed sometime shortly later in combat. The Red Baron earned his name from (apart from being an actual baron who was kicked out of the cavalry corp) painting his fokker bright red in an attempt to attract more fights from enemy pilots. This lasted about a week when it became apparent that too much attention wasn't a good thing. From then on the Circus made do with streaming scarfs from the tension wires in their wings, each pattern unique to each pilot.
The baron himself wasn't known for his flying prowess, although he was more than competent for his time (pilot training was inadequate at best, and horrifyingly short more likely) but for his gunnery. He characterized and set up the archetype for the gunnery-type fighter ace. His primary technique was to fly behind his enemy but off to one side, then use the rudder to turn his plane sharply and fire a burst from the side, where his opponent probably thought he was safe. Gurring was his second-in-command when the baron was killed, and so is how Gurring won enough fame and support to become head of the German Luftwaffe, although he was not actually a popular leader within the Circus.
Enough with the history for now. The colors of No.4 and 5 remind me of the old pre-war USAF schemes on their P-26 Peashooters and Devastators, although I dislike the double pattern on the tailplane of No.5. No.3 also looks mighty fine, perhaps with a blue primary strip with brass secondaries instead of copper, the ivory white look can stay.
In all, a toss up between No.4 with No.5's darker blue, or No.3 with blue and brass stripes. Maybe our sister squadron, the 22 Emeralds, can take the second favorite scheme?