When summoning an arrow that has multiple potion effects (such as by the potion_contents component) the summoned arrow will produce particles of only one color.

This is in contrast to players and other mobs, which produce multiple colors of particles when they have multiple effects applied.

Example command:

summon arrow ~ ~1 ~ {item:{id:"minecraft:tipped_arrow",count:1,components:{"minecraft:potion_contents":{custom_effects:[

{id:"minecraft:speed",amplifier:0,duration:200}

,{id:"minecraft:regeneration",amplifier:0,duration:200}]}}}}

This issue is potentially related to MC-273875 which also deals with tipped arrow potion effect particles.