Orange, green and purple were intentionally chosen and made to match the 3 colour variants that the older generation of Scream Fortress effects used (V-VI). That's all.

Do unusual creators know any colors besides these 3??

dapper dickens spotted

Really cool but i think you should remove the purple one and maybe even the green one

It works as expected: https://imgur.com/a/ulmCtwk

out of curiosity, but how this effect would like during sniper's melee taunt?

love it