Lucid

Whilst this can theoretically be achieved on any level my recommendation would be Level 19 as this level starts with a chain of 40 yellow blocks. After clearing these try to stick to sets of two blocks at a time to minimise your scoring until you reach the required 60 yellow blocks.

The achievement will unlock in game as soon as you clear the 60th block.

If you haven't already unlocked this there are the required number of blocks on screen at the start of Level 30. Just clear from the top of the screen down so you don't separate any blocks.