I looked up the Shimmering Triangles pattern. It's a very pretty pattern. I have motion sickness so it would never work for me. Might want to check & make sure there is no motion sickness in the couple. When I was looking up the Shimmering Triangles, I saw a pattern called Shimmering Strata. To me it is a very modern quilt that already has the gray background and could easily be done with the colors you are talking about.
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My daughter & I made one up similar to this with a black background and multiple colors. We designed it ourselves based on a picture she found on the internet. Our quilt was made as 2 stripsets of 3 inch finished strips of color, with ten colors per set. Very like a bargello. We then sub-cut them into different widths and then alternated the colors with black on all the ends filling in the extra length. It is meant to be viewed vertical, not horizontal.