A 6x6 board rated steady logic, level 51 of 300. Catdoku levels are identical for every player, so this solution always matches the board in your game.
The level 51 board
Place one cat in every row, every column and every colored patch. No two cats may touch, not even diagonally.
Level 51 answer
Row 1: column 6, in the yellow patch
Row 2: column 2, in the sky patch
Row 3: column 4, in the rose patch
Row 4: column 1, in the mint patch
Row 5: column 5, in the lilac patch
Row 6: column 3, in the peach patch
How to solve level 51, step by step
After every placed cat, cross out the rest of its row, its column, its patch and the four corner squares around it. The steps below assume you do (the in-game auto-paws assist does it for you).
Cat 1 of 6: the peach patch is down to a single free square at row 6, column 3, so its cat settles there.
Every free square of the yellow patch sits in column 6, so the yellow cat must come from there and the rest of column 6 can be crossed out. Every free square of the sky patch sits in row 2, so the sky cat must come from there and the rest of row 2 can be crossed out. Cat 2 of 6: the yellow patch is down to a single free square at row 1, column 6, so its cat settles there.
Every free square of the lilac patch sits in column 5, so the lilac cat must come from there and the rest of column 5 can be crossed out. Every free square of the rose patch sits in column 4, so the rose cat must come from there and the rest of column 4 can be crossed out. Cat 3 of 6: the sky patch is down to a single free square at row 2, column 2, so its cat settles there.
Cat 4 of 6: the only free square left in row 3 is column 4, so the cat goes there.
Cat 5 of 6: the lilac patch is down to a single free square at row 5, column 5, so its cat settles there.
Cat 6 of 6: the mint patch is down to a single free square at row 4, column 1, so its cat settles there.