Most guys I've seen have actually been wearing black suits. Younger people look sharp in black suits and while it may not be generally the best thing to do on a sunny day, it certainly won't kill your chances at an acceptance especially in winter weather; many navy/dark grey suits will look black on a bleak day from a distance anyway. Up close, they'll be looking at your shirt and tie more than they'll be looking at your jacket. When you sit down, you unbutton your jacket which makes it even less likely that they'll be distracted by your black suit (which again, looks fine on most young men).
If you're looking to cut costs, OP, you can stick with what you have. If you want to mix it up a little, I'd start with the shirt & maybe the tie depending on how much color you want to add to the outfit.
If you really want to buy a new suit, go for it but it takes a while to pick one that fits properly, you have to get a shirt/tie to match the new suit, and it's expensive on top of that. Your black suit isn't even a terrible option.
It's up to you and your bank account. H&M's suits are too casual for me and I'm not a fan of two-buttons. Ditto with Zara which also offers cheap but casual suits. Men's Wearhouse is a typical place to go. Macy's can also offer lots of styles to try out just to see how they fit.