You know those shells that disappears when you interact with them? You have to find all of them. At a certain place in every chapter(except last chapter and the 'dark' chapter), there's this wall that shows the currently collected shells, and uncollected shells. It even shows you what chapter you'll have to visit to find it. After you collect everything, you'll be able to touch the wall of shells, thus making you, glowing blue-white. I won't spoil all the special features of that suit, but I'll tell you one. Do you know the 'golden boost?' You can use it if you press the boost button 3 times rhythmically. Well, with the blue diver suit, if you hold on to the boost button after your fins turn gold, your fin will stay golden, and you'll be swimming faster than the shark that you can see where the shark model disappears during the runaway. And, the color is absolutely gorgeous during the final chapter, where originally, your suit turns gold

some shells are extremely well hidden. You'll have to look around a long time to find all of them. But at the end, it's totally worth it. I'm so used to the blue suit that the original black suit feels painfully slow to me

here's a sneek peek of what'll happen