Assume that your range is A1:A10.
Select the range, go to FORMAT > CONDITIONAL FORMATTING
in condition 1 box, you will have 'cell value is', in the next box select
'equal to', and enter the following in the 3rd box: max($A$1:$A$10). Click
on format and select green in the pattern tab (third tab).
Then Click 'ADD' to enter the second condition. This time enter min($A$1:$A
$10) and select red color.
Click ok. Note that the above formula should not be inside double quotes in
the boxes mentioned as above.
Mangesh