Lurking within the M1’s base are 21 surface-mounted LEDs...
...The downside is the visibility of the individual LEDs, which is so prominent that you can basically count each one. This isn’t an issue from a top-down view, but from the sides it makes the RGB glow look unnatural.
If I had to guess, they probably went with only 21 LEDs around the edges so that they could use an existing keyboard RGB controller that was designed for boards with up to 105 keys. It would probably be better to have the spacing at least as close as the LEDs under the letters, but that would require around twice as many edge LEDs, which might not be supported by readily-available keyboard hardware.
I tested the Sakura Pink version of this keyboard, which already looks busy sans RGB, with pink flowers and accents. It was hard to find an RGB effect that enhanced this design rather than overpowered it. And it was hard to tell what was the base’s RGB effect and what came from the keys. The black version and, especially, the white version with its white pudding keycaps seem to blend with the RBG effects better, based on the pictures Marsback has provided.
My first thoughts looking at the top photo were either "blood spatter" or "spilled wine". It doesn't really look bad, but the soft RGB seems to be in conflict with the cherry blossoms. Perhaps some shade of faint pink or violet backlighting might look better though. Judging by the images, the solid white keycaps probably look the best. Of course, I've generally not been a fan of excessively distracting RGB, at least for something I'm going to actually sit down and use for an extended period. I would probably turn the brightness way down low and set it to a fixed color, or turn it off entirely, though that would kind of defeat the purpose of going with a keyboard design like this.
One other thing I probably wouldn't be totally fond of is how thick it is. That looks like a rather thick keyboard, and could have probably benefited from a matching wrist-rest on the front.