Now I want to highlight the third column with same color irrespective + and - ve values (tried with conditional formatting, same color option is not available to highlight +ve and -ve values in same color- Red color).
You can rather create a new line item (number formatted) and make the applies to none (To reduce size), then put 1 in the formula bar. Now use this line item to conditional format the 'Variance' line item.
In addition to the earlier responses, if you only want to color when the variance is above a certain treshold, then you could use the ABS (absolute) function on your variance value instead of just inputting 1, e.g:
IF ABS(Variance) > 10 THEN 1 ELSE 0
or if you want the color scales, you could ofcourse simply use: ABS(Variance)