Description

Makes the wolf collar into a high-resolution rainbow. Works best with white dyed collar. If you want this to be the default, use the folloring command in a repeating command block. Note that this command will make every wolf's collar white, and the rainbow is only visible with the resource pack. You can replace the @e[] with a target selector or your wolf's UUID to only apply it to certain wolves (or just use white dye).
/execute as @e[type=wolf] run data merge entity @s {CollarColor:0b}

Versions

Supports Java Edition 1.21 - 26.2 (older versions untested)

Compatibility

Incompatible with anything modifying the wolf collar texture. Use white dye for best effect. Higher resolution than the normal texture.