Well as you have already decided to use a blue colour to highlight elements that are active, like your toggle switches in the other columns, then it might be best to use that colour to highlight active filters too.
Option 1: Make the whole filter element background blue
Benefit of this option is it works well for other input elements, not just text input.

Option 2: Make only the input elements blue
Benefit of this option is you can apply it to only 1 part of this filter if you allow open ended ranges. For example, 10 to any.

Additional Suggestion
Just a thought, but it might also be worth considering hiding the "clear filter" option unless there is actually a filter value specified. This will help de-clutter the UI and also helps to further highlight which options have filters applied.
If you are concerned about the extra whitespace between options when the "clear filter" link is not visible, then you could consider moving it somewhere else. For example:
