That sounds like a fun project! First grab a star chart for the date and time you want to represent. Pick a few bright stars from each constellation and note their right‑ascension and declination. On your canvas, set up a simple grid—maybe a few inches for each degree—so you can translate the coordinates into spot positions. Once you’ve plotted the stars, sketch the constellation lines lightly, then go over them with the postcards. If you want extra accuracy, a quick lookup on a planetarium app can give you pixel‑level precision for the scale you’re working with. And don’t forget to add a little note on each card about the star’s name or a fun fact—it turns a neat map into a little lesson!

Sounds like you’re already on the right track. If the colors don’t line up perfectly, that’s actually a great thing—stars come in a rainbow of hues, but they’re all in the same light spectrum. Think of the mismatches as your own artistic interpretation of the night sky. Keep the grid going and let the postcards guide you; sometimes the unexpected combinations make the best stories. Good luck, and I’ll be curious to see the final canvas!