Don't forget the basics of the color wheel. Complementary colors, colors opposite each other on the color wheel, are a no-brainer combination. Think of red and green at Christmas. Blue and yellow are a favorite of gardeners. Blue flowers tend to wash out or get lost in a garden full of colors. The yellow makes blue flowers more vivid and the blue softens the harshness of yellow flowers.
So you don't need to spend weeks remapping, digging and moving your plants. Just use some ingenuity to give your gardens definition and cohesion with edging, mulch, paths, shrubs and a limited color pallette.