The other significant difference was that Jackson regularly wove in a message of inclusion and equality. In the examples below (all of which are slightly modified scans taken from the Billy Ireland Museum) you can see a number of examples where white American officers express very negative attitudes towards Speed which, in turn, he repsonds to with a mixture of resignation and quiet strength. He repeatedly tolerates the poor behavior, and then tries to prove how wrong people are about Blacks by just being a better hero than the white soldiers.
Of course, just being a better hero is a whole lifetime of issues to unpack. To those who've had to deal with it at all, the notion of having to do twice as much 200% better than their white counterparts in order to be given half as much is a refrain they've had to live their whole lives with. From what I've seen/read of the strip, though, Jackson himself didn't address that other than it was a simple matter of fact. I can only guess that in the 1940s, Jackson didn't feel he could hope for a loftier victory than just even having the chance to be treated as an equal. The dialogue is often a bit ham-fisted, but only in the same way many comic strips of the time were.
But there's another element at play here which seems to be handled with much greater subtlety. Speed's girlfriend in the initial installments was a Black schoolteacher named Carmen Brooks. I don't know what happened to her, but by the time we get to the sequences below, he's found a new love interest in Minta Washington. I can't find an instance where her actual heritage is expressly named (other than she's not Italian) but she's clearly identified as a European blonde. So she's not an American, but still decidedly pretty white. And she's seen here first holding hands (in the fifth piece I reproduce below) and then kissing Speed (in the eighth)! And in neither instance is any particular attention drawn to it; it's just two people interacting somewhat romantically.
Now, that Minta isn't American probably assuaged some possible concerns about showing an interracial couple (not to mention the fact that the strip only appeared in African-American newspapers) but Jackson still threw it out there as a completely normal and casual thing. In 1943, nearly a quarter century before Loving v. Virginia. Amazingly progressive, and extremely deftly handled, I think.
Maybe some of Jackson's overt messaging was a little over-the-top, but I wonder if that was done deliberately to slip these other elements in more surreptitiously. Distract readers with an obvious issue, and slide another one past them while they're complaining about the first. Maybe? I don't know. Frankly, I can't find hardly anything written about Jay Jackson, and even less on Speed Jaxon. I've only been able to find about 30 strips online, and can't even pin down when it first started or stopped. Which is a shame because Jackson seemed to know what he was doing, and creating an entertaining and progressive comic strips besides!