Possible theory.

So with Bad Batch about to end in a few days, I feel like I need to say this. In episode 15, Echo managed to infiltrate Tantiss with a TK/Phase 1 Stormtrooper armor. and seeing Echo without the helmet reminded me of Conspiracy Arc of The Clone Wars with Fives taking a clone rookie's armor and dying in it. and this is where the theory/possible scene occurs.

Echo will die wearing the armor and it's significant to his past as a member of Domino Squad. The squad who the trainers at Kamino thought they'd never pass but they did. The first three (Droidbait, Cutup, and Hevy) died at the citadel with Hevy sacrificing himself to warn the Republic of a possible attack at home. Echo and Fives later joined the 501st and following the attack on Kamino, became ARC troopers. They would later go on the Citadel which Echo "dies" trying to take and use the shuttle. But unknown to anyone and Fives, Echo did survive.

Fives thought he was the last of the Dominos and continued to fight for the Republic and for his brothers when Pong Krell action's nearly got them killed. Then came in the Conspiracy arc, Fives learned of the chips and their possible usage, he tried to warn and went against the republic which he's trying to save but ultimately, it was not enough. Despite Rex's and Kix's attempts, the chip's true purpose remained a secret.

Echo was turned out to be alive following Rex, Jesse, and the Bad Batch's discovery and with the help of Anakin, later rescued the now distinctly different ARC trooper. Echo would later bring a victory to Anaxes thanks to his cybernetics and joined the Bad Batch at their offering and Rex's allowance. He survived Order 66 and with the Batch, deserted the now newly created Empire. Then it was mercenary work and the Clone resistance to help the clones the Empire is now discarding which he and Rex created and now, Hemlock's experiments on clones which Echo is determined to find, destroy, and rescue his brother and most importantly, his sister; Omega.

and now we're on the Endgame on Tantiss and what is this I'm talking about... Echo will die wearing the clean white stormtrooper armor the same way Domino Squad did, in their white clean armor. (Hevy, Droidbait, and Cutup died in their first duty, and Fives died wearing a rookie's stolen armor) Domino Squad was supposed to fail in Kamino but they persisted and one by one they died wearing their white armor except for Echo who was wearing his ARC trooper armor during the Citadel. Now, with the white armor, the last of the Dominos is about to fall.

tl;dr Echo wearing white armor signifies how he'll die and connects his past as a member of Domino squad.

EDIT: With this, I just noticed that it's not just the armor and how they'll die, It's the fact that all before Echo died for their brothers, Hevy, Droidbait, and Cutup died but it wasn't in vain, the Republic knew of the CIS plans to attack Kamino which they later defended, Fives died trying to save the Republic and his brothers from the Sith's plans but it wasn't all in vain, Rex's complaints were heard by Ahsoka which resulted in her removing the chip from him and in turn, the Batch including Echo's... then it is now Echo's turn to save his brothers from the Empire and experimentation from Hemlock.

Domino Squad is more than just a group of clones dying one after the other, their deaths played a role in trying to help protect the clone army as a whole.