Question : write a IF_And_Then, OR statement correctly

Hi everyone,
I have a pesky little conditional statement that is supposed to check for two possibilities and perform a calculation based of its findings, or if it did not find either possibility then return a "", null value.
Here is the  line: =IF(AND(O7<>"",I7="sell"),K7-O7),IF(I7="buy",O7-K7,"")

The statement is supposed to check "O7" and if it is <>"" then check to see if iit is "Buy" (if tthe calculation is positive it  colors the row green, if negative it is colored red) or "Sell" and perform the proper calculation, if neither is true the cell should remain blank and the row uncolored.
Thank you for your consideration.

Answer : write a IF_And_Then, OR statement correctly

You might consider testing O7 by itself:
=IF(O7="","",IF(I7="sell",O7-K7,IF(I7="buy",K7-O7,"")))