I feel your pain. I see that using styles apply to the entire paragraph.
So I have a kluge until some really bright minds step in.
Open the Pages document that you need to edit.
Have in memory a single word that is in (red) in your desired font style.
Just type a word in (red), make your font color adjustments. Copy the (red) word into memory. Delete from the document. I put this in parantheses.
Paste the (red) word where you want to make an edit
Sample
I have to edit papers that require me to type red words into each sentence, sometimes several times per sentence.
Every time I write a word in red, the next time I click into the sentence (or anywhere else on the document), the color defaults back to black.
So let's say you want three edits. I am showing all three, but you'd just do it as you encounter things that need correcting.
Sample
I have to edit papers that require me to type red words into each sentence, sometimes several times per sentence (red).
Every time I write (red)a word in red, the next time I click (red)into the sentence (or anywhere else on the document), the color defaults (red)back to black.
Type directly into the(red) or double click on red and make your edit(s) one at a time.
Result
Sample
I have to edit papers that require me to type red words into each sentence (only those that needs correcting), sometimes several times per sentence (that sounds painful).
Every time I write (you mean type, not write) a word in red, the next time I click (with the mouse)into the sentence (or anywhere else on the document), the color defaults (reverts) back to black.