Why do this
problem?
This problem is one that requires working systematically.
It is a good activity for promoting discussion between learners
working together and also for giving encouragement to those
whose spacial ability is better than their numerical
achievements.
Key questions
Which row and which column have none of that colour in them?
Have you checked the diagonals as well as the rows and
columns?
Possible extension
Learners could try other-sized squares such as $4\times 4$ and
$6\times 6$. With some squares it is possible to place one
colour correctly but no more. Of which sized squares is this
true?
Possible support
You could suggest starting with just one
colour, then fitting in the other colours, one at a time.