These colors create continuity as they share a common color. Adjacent colors are side by side on the colorwheel. These colors harmonize and blend together. Mint green with an accent of bright blue can work well for water scenes. Use the middle color as the predominant color and the other colors for accents.
Different shades have more of certain colors than others.
Terra cotta is a very orangey brown, mustard brown would have more orange and yellow. Some more suggestions Color can be added with paper, diecuts, colored pens. Make sure that whatever you use contributes to your color scheme and theme, instead of detracting. Add you accent color to frames by placing it under a punched-out shape in the corner of your frame on on it with an appropriate sticker. Use vibrant blue, red, and yellow for the most striking color combination.