You asked for harder puzzles - we've got them! The color gradient jigsaw puzzles in the Blue Kazoo COLOR series are nothing short of addictive
RAINBOW COLOR WHEEL — 1,000-piece Color Gradient Jigsaw Puzzle
Iridescent Glitter Flow Jigsaw Puzzle by Ma Perez - Pixels
Gradient & Rainbow Collection – ENJOY Puzzle
Buffalo Games - Drops of Color - 300 Large Piece
Glitter challenge 1000 pieces Ravensburger : r/Jigsawpuzzles
Puzzle Galaxy Rainbow Star Print Jigsaw Puzzles Table
Color Fold, 1000 pieces, Professor Puzzle : r/Jigsawpuzzles
1000 Pieces Jigsaw Puzzle - Colorful Gradient Swirl (1236) – ENJOY
Gradient 1000 Piece Puzzle – Vital Industries
Cloudberries - Gradient Puzzle (1000 Pieces) : r/Jigsawpuzzles