Xio’s game didn’t copy any art assets from anywhere, as I can tell you, since I made all the art for it. [Mostly over one weekend, as a volunteer favor to the developers.]
The colors were not copied from anywhere, they were picked, by me, with no reference to any existing art, using a careful process designed to maximize distinguishability. To be specific, I decided that the colors should all be clearly separated in CIELAB lightness and hue, and then chose which lightness to match to which hue based on the gamut of then-current iPhones.
The result is a bunch of “bright” colors. But lots of games want bright colors, because they are the most easily distinguishable, and having easily distinguishable colors makes a game easier to play.
As for the appearance of the bricks, I cooked up a dozen or so possibilities in Photoshop, and let the rest of the team decide which to use. Again, created in a few various styles, but not with any reference to any previous game.
Just look at the screenshots of Xio's clone and Tetris. They are almost identical. Now compare Tetris with tetris-likes such as Dr. Mario, and the difference is immediately apparent.
Copying assets doesn't just mean verbatim copy-and-paste. It includes recreating other assets such that they are virtually identical to the source material, as the art assets you apparently created were.
The colors were not copied from anywhere, they were picked, by me, with no reference to any existing art, using a careful process designed to maximize distinguishability. To be specific, I decided that the colors should all be clearly separated in CIELAB lightness and hue, and then chose which lightness to match to which hue based on the gamut of then-current iPhones.
The result is a bunch of “bright” colors. But lots of games want bright colors, because they are the most easily distinguishable, and having easily distinguishable colors makes a game easier to play.
As for the appearance of the bricks, I cooked up a dozen or so possibilities in Photoshop, and let the rest of the team decide which to use. Again, created in a few various styles, but not with any reference to any previous game.