I have several suits. My go-to suit, and the color may be debatable, is my solid black suit with light blue tie and pocket square. The shirts with this are interchangeable. I just bought my newest addition, with leather-soled shoes, for $1,000. If you want to look like you know what you are doing without flaunting it buy real leather-soled dress shoes and a decent Swiss-made watch. You can get a Tissot or Victorinox for around $500 (cheaper online) and a stainless steel band will go with anything. It may be expensive but this combo will last 10 years without going out of style.
Whoever said all suits must be tailored is correct. There are no exceptions. If you think you have an exception you are wrong. I would rather spend $50 on a suit and $200 on tailoring than $1,000 on a non-tailored suit.
With that being said, a dark charcoal gray is probably the best all-around suit color but I wear black because it hide its flaws better. I wear a tan/light brown suit for events like Easter or a graduation to keep it dressy but not so "business-like".
Men have little room for personalization so don't skimp on shoes or the watch because that's all we really get. A $400 pair of Allen Edmonds is going to look better and hold up against style changes more than $75 on-sale from JCPenney.
Don't wear a blue blazer with khakis for a mid-level interview because it looks too casual. The only salvation for that is if it is winter and you add a sweater to the ensemble and your shoes are good quality.
Most men dress really bad. Once you get a good suit tailored you'll notice right away how many men at conferences have coats that are two sizes too big and it makes them look sloppy.