Can I sub-total 2 of 4items in a column in a pivot table?

[Jenzz22]

So for this example data:
a b
1. 4 Red
2. 6 blue
3. 5 green
4. 8 yellow

I want the output to be -
Red 4
Blue 6
Green 5
Yellow 8
Red + Blue - 10

Is there a way to do this in a pivot table?

Thanks