Fence colors to avoid are anything that creates a real clash and colors that you rarely find in nature. Black can be a very harsh color in a garden and usually only works in a very minimalist, contemporary spaces. Vivid primary colors like yellow and red do risk dominating and being over-stimulating in a place that you probably want to feel calming and serene. Stick with more muted versions of colors – sage greens, soft navy blues, muted reds, and yellows.