MsOf10 Sum of 2 rows (Used Range), check negative (VBA)

Not sure how to describe this but I'll give it a go:

If have 3 rows: A, B C

Example:

* A B C
1 5 4
2 7 1
3 3 7
4 2 1

Now I want to do a sum of Col.A MINUS Col.B >> Answer in Col.C >> If Col.C is negative, then color.
When using my example, Row 3 should be colored.

I hope someone understands what I'm trying to do.

Thanks in advance.