Apple often refreshes Apple Watch band colors on a seasonal basis, and code in iOS 17.4 suggests that new spring colors will be coming soon.
As found by MacRumors contributor Steve Moser, the spring colors include Light Blue, Ocean Blue, Pink, Raspberry, Soft Mint, and Sunshine (likely a light yellow). There are also two Hermes colors, Bleu Céleste and Jaune de Naples.
When released, these colors will be available for watch faces that support different color options, and they'll be listed in a Spring 2024 section in the Apple Watch app on iPhone. Right now, the colors are not showing up there.
Apple often also uses these same colors for new iPhone cases and iPad cases. If we get a spring event this year around the end of March, we can expect to see these band options and possibly new cases that offer the same colors.