Coincidence:

( Mairead C has been considered as Chloe's replacement. However it doesn't mean anything be as similar although it does for these only these two. Except infact this happened not once but twice on Carlin's part on DVD specials.)

Here's an overview below what I mean:

Chloe Agnew

Song's from the Heart
White Dress: both solos (When You Believe and Galway Bay)
Pink Dress in Duet (Pie Jesu with Lynn)

Mairead Carlin

Destiny
Blue Dress: both solos (I See Fire and Like an Angel Passing Through)
Red Dress in Duet (Ride On with Eabha)

Ancient Land
Midnight Blue Dress on both solos (Ae Fond Kiss and County Down)
White Silver Dress in Duet (Over the Rainbow with Megan)