I love Hobo bags!
Im going to say " red" because it's a more fruity red and summery, but not over to peach or coral, it's still red enough, and you are planning to OD on your citron capsule, and you want super happy contrast, and the poppy is more that than the blue and yellow pairing. Also I'm thinking it's actually a little bit harder to find this color than true red, burgundy and so on.
Next I would normally say blue because it works with everything, but I don't like it in patent as well, it's fun but plasticky and does make me think of pool toys, which are fun, but I like more mystery in blue leathers. However, just to keep up the indecisiveness, the blue IS " cool" and cools off your warm palette, so says summer via heat- antidote as compared to summer- spicy.
So citron is a contender, though you may have little need of such a small pop of citron, it is nicely assertive with anything the least bit less colorful, can masquerade as cognac on speed, and is unexpected( for most people) and zingy with all of your red items.