Connect the Blocks!

Can you find the path between every pair of coloured squares on a grid? The only rule is that paths can't cross over! Puzzles range from relaxingly simple to fiendishly hard depending on the size of the board. Each grid has a solution and a par score - see if you can make a more efficient set of paths than the computer! Easy to understand but difficult to master. 

(Your solution also creates a nice abstract Mondrian-esque art piece)

There's 250 puzzles in each of 6 different sizes.