SlideMagic uses a simple colour scheme: (just) one distinct accent colour and lots of shades of white/grey/black.
What are good accent colours?
One that stands out
(This is the tricky bit):
One with good contrast with white
One with good contrast with black
One that fits with your brand and/or industry, or the opposite one that really sets you apart from everyone else in your industry if that is what you want to do.
One that you like
People often forget about number 2, which cuts off a lot of creative possibilities with your design
Photo by Daniele Levis Pelusi on Unsplash