How do I clean my Apple Watch pink sand sport band?

See this article: Cleaning your Apple Watch - Apple Support

Clean and dry your band

Remove the band from your Apple Watch before cleaning. This cleaning information applies to Apple-branded bands only. For all other bands, follow the care information provided with the band.

For leather bands:

1. Wipe the leather portions of the bands clean with a nonabrasive, lint-free cloth. If necessary, lightly dampen the cloth with fresh water.²
2. Don’t soak leather bands in water. The leather bands aren't water resistant.
3. Let the band air dry thoroughly before you attach it to your Apple Watch. Don’t store leather bands in direct sunlight, at high temperatures, or in high humidity.

For all other bands, buckles, and closures:

1. Wipe the band clean with a nonabrasive, lint-free cloth. If necessary, lightly dampen the cloth with fresh water.
2. Dry the band with a nonabrasive, lint-free cloth before you attach it to your Apple Watch.

At the bottom there, it mentions:

For all other bands, buckles, and closures:

1. Wipe the band clean with a nonabrasive, lint-free cloth. If necessary, lightly dampen the cloth with fresh water.
2. Dry the band with a nonabrasive, lint-free cloth before you attach it to your Apple Watch.

I would try that. Anything more harsh might cause the color to fade.

Remove from watch and I use an old toothbrush with a bit of dish soap, rinse well and allow to dry. Works great for my bands.

You can also try the Mr. Clean Magic Eraser. I've used it.