Trademarks are not limited to text, the gray and yellow color scheme is a
Registered Trademark by Fluke [0]. Nowadays 2/3 of the cheap meters use this color scheme, at this stage this trademark is effectively dead, most people will not connect this color scheme to Fluke. I didn't even know it came from Fluke (neither did SparkFun I guess), until this incident.
But unless Apple registered something similar for shape or the color of the AirPods, or somehow patented its design, it's not an infringement, and the CBP cannot seize them.
Now the question is, how much does it cost to sue the CBP...
[0] https://tsdr.uspto.gov/#caseNumber=75934005&caseType=SERIAL_...