I switched to the colored bass strings years ago and wouldn’t go back to the copper if you paid me.
I’m sure some people can hear a difference, just as some people find CDs to be so inferior to vinyl. But those aren’t most people and if there is a difference it is so slight as to be irrelevant. The only way to notice it is if you had someone with exceptional hearing listening to two harps with the two different strings playing together side by side.