A 6x6 board rated fiendish, level 75 of 300. Catdoku levels are identical for every player, so this solution always matches the board in your game.
The level 75 board
Place one cat in every row, every column and every colored patch. No two cats may touch, not even diagonally.
Level 75 answer
Row 1: column 5, in the yellow patch
Row 2: column 1, in the sky patch
Row 3: column 3, in the rose patch
Row 4: column 6, in the mint patch
Row 5: column 4, in the lilac patch
Row 6: column 2, in the peach patch
How to solve level 75, 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).
A cat at row 2, column 2 would leave the rose patch with no home for its cat, so cross that square out. A cat at row 2, column 6 would leave the mint patch with no home for its cat, so cross that square out. A cat at row 4, column 3 would leave the rose patch with no home for its cat, so cross that square out. A cat at row 4, column 5 would leave the mint patch with no home for its cat, so cross that square out. A cat at row 5, column 2 would leave row 6 with no home for its cat, so cross that square out. The yellow, sky, rose and mint patches all squeeze into rows 1, 2, 3 and 4, so those rows are reserved for them; every other square there can be crossed out. The sky and peach patches all squeeze into columns 1 and 2, so those columns are reserved for them; every other square there can be crossed out. Cat 1 of 6: the only free square left in row 4 is column 6, so the cat goes there.
Every free square of the rose patch sits in column 3, so the rose cat must come from there and the rest of column 3 can be crossed out. A cat at row 2, column 3 would leave row 3 with no home for its cat, so cross that square out. Cat 2 of 6: the rose patch is down to a single free square at row 3, column 3, so its cat settles there.
Cat 3 of 6: the only free square left in row 2 is column 1, so the cat goes there.
Cat 4 of 6: the peach patch is down to a single free square at row 6, column 2, so its cat settles there.
Cat 5 of 6: the lilac patch is down to a single free square at row 5, column 4, so its cat settles there.
Cat 6 of 6: the yellow patch is down to a single free square at row 1, column 5, so its cat settles there.