Set conditional formating to Excel

Set a conditional format in Excel to change negative numbers text color to red.

Set a conditional format in Excel to change negative numbers' text color to red.
The code can be modifeid quite easly to set any other condition.
Example:
a=randn(100,1)
xlswrite('a',a)
xlsCondFormNeg('a','Sheet1','A1:A50')

This Example will set the conditional formating to the first 50 numbers in the column.