How do I write a positive/negative and red/green function?

I'm trying to make a "weight-based" spreadsheet. I want to show a difference between numbers so if an item lost 5 lbs, there would be a "-5" and it would be in green font showing good.

For example, a box weighs 20 lbs and then drops down to 15 lbs. This would be a good result. So I would have 20 lbs in A4 and 15 lbs in A6 and I want to show the difference in A8. However, since I want the box to lose weight, I want it to show a negative value of "-5" in green font meaning it is good. And vice versa, I want it to show "+3" in red font if the box gained weight.

I can't really figure out how to get the signs working properly. I'm assuming to use an "if" function in where if the difference is a loss, show the negative sign and have it in green font. And if the difference is a gain, show the positive sign in red font.


I hope this wasn't confusing.

Formula in A8 would be

=A6-A4

One way to get the font colour is to use a custom number format for A8

[Red]"+"General;[Green]-General;General

Alternatively you can use Condition formatting. Testing for a value Less Than 0.
Use formatting of Font-Green.

If you want 0 in black then add another condition for Greater than 0.
Otherwise format the cell as having Red font