This is a great APOD! I love how the fine colors help us assess the nature of this galaxy.
Note the yellow population of NGC 7424. This is the old, stable population, billions of years old. NGC 7424 is strongly yellow in the bar and between the bar and the innermost arms, but it is also quite yellow below the lower innermost arm. There is what looks like a long, soft "arc" of yellowness below that innermost arm. It is as if we were looking at a broad yellow arm, made up almost exclusively of an old yellow population.
Look closely, and you'll see a similar broad soft arm above the upper innermost arm, too. This broad soft arm is fainter than the "yellow arm" below, and upper soft arm is not quite as yellow. Note, however, how regular these two soft broad arms are.
By contrast, the star forming arms and areas are all "Sturm und Drang" and rock and roll, wild and crazy and irregular. Clearly these are a recent addition to the galaxy, and the soft broad arms represent the underlying mass distribution and rotation of the galaxy. The bright starforming areas are extremely bright, but not so massive. Luminosity increases exponentially with mass in stars, so that a few massive stars can outshine millions of low-mass stars whose combined mass is thousands or millions of times greater than the cluster of hot brilliant stars.
This galaxy looks very "wind-blown" to me. Its original structure seems to be relatively unchanged, but wildfires rage on the surface of it, creating turmoil and fireworks and weird shapes primarily beyond the well-established old spiral structure.