For example, red if the size increased, and green if it decreased?
Here is an example how it appears now:
(-50%)
(-12%)
(+120%)
(+2%)
(-5%)
(-78%)
(-45%)
(+40%)
(-15%)
Here is an example how it could appear:
(-50%)
(-12%)
(+120%)
(+2%)
(-5%)
(-78%)
(-45%)
(+40%)
(-15%)
Doesn't that make it easier to see which files grew and shrunk in size?

To be safe, this shouldn't be a "default" or even a hard-coded feature. I think it would be better as a option that someone can enable in the Batch Convert settings. (This is a safeguard just in case someone is using a theme that doesn't work well with colored text.)