Dark colors at dusk and night, especially in muddy water. It should allow the fish to see the contrast and/or shadow or outline of the bait. Daytime and especially in clear water use light colors, smaller baits and lighter line. I started casting a couple months ago with 1" sliders on 1/32oz jig heads with 4 pound line when in clear water. My numbers of hits and fish caught per cast has doubled.
Dumb Crappie don't grow to 15 inches without being caught. The hits near dark is probably because the Crappie can't see the bait, your fishing line or an angler as easily.