Have you ever looked at an outfit, or a textile, or a paint color, and know that it just says "1970", or "1985"? How does that happen? When you see a TV commercial or poster in a retro style, do you wonder how they get the colors to tell the story? How do you know the colors you choose now will go with your wardrobe next season?
One place to start is Pantone.com. They have indices of the "on trend" colors for spring and fall for men and women for the last three years. These color palettes can help you choose colors to coordinate with clothes that your garment will be worn with in the future. If you choose to combine colors from any individual palette, you will be telling the color story of the season. Different seasons tell different stories, so if you don't like the story any particular season tells, switch to a different palette.
If you Google (click the Images browser once you're in Googel) some of your ideas plus the word colorwheel, you may find what you're looking for. I did that with 1950s and Colorwheel, and I came up with the colorwheel for the Edsel automobile. It shows a very subdued, plant based palette that was typical of the early 50's. Just about any combination of these colors will evoke a retro feeling, and coordinate in a familiar way.
Here is a link to one of my Pinterest pin boards. There is a distinct lean toward one palette, and the only piece that doesn't fit is the Matisse poster. If I were to choose colors based on this board, they would reflect my own personal taste and style without being tied to a particular era.
You can pull up a color wheel on the computer as well. Colors directly across from each other are called complimentary colors, and they tend to accentuate one another. Green next to red looks a whole lot greener than green next to turquoise.
Another way to accentuate a color is to combine it with itself. Try a dark and light version of the same color, or two versions of one. Fern green and sage green, or either of those with some pine green would make an interesting combination.
Not feeling confident combining colors? Combine a color with cream, white, or grey. The color will look classic and crisp. Not the classic kind? Pull two colors you like from an object like a lunchbox, or some packaging. Still nervous? Ask a friend or store clerk to guide you.
If you're still unsure, make a swatch in your colorwork pattern. If you want a little more or less contrast, it will become clear very quickly. With a little practice, you'll find your confidence increasing!