My most productive color over the years has been perch scale, followed by orange with black dots, and silver with a black back. These little plugs are too small to cast on spinning gear without added weight, so place two split shot about 1 foot apart on your line starting about 1 foot above the lure. If you use only one split shot, casting tangles will occur. A pair of size BB shot will do for an average-size stream, but go up or down in size as needed to get the lure deep. That big snap-swivel you might use with heavier gear looks ridiculous when pegged to a miniature spinner.
Trout think so, too.
But some lures require at least a snap, specifically minnow plugs and many spoons with a split-ring at the lure eye. These little rings have sharp corners that can sometimes cut fine monofilament when you knot the line or when a fish strikes. Once again, fish up and across in faster, deeper water and at the heads of pools. Allow the lure to sink and drift with the current as you keep a tight line, barely bringing action to the plug. The Flatfish's distinct vibration when retrieved is easily felt at the rod tip and means the lure is working correctly.