I've not tried this per-say but if you add color to the Text image atlas that PromptLocal uses you might be able to add color. Though all your text commands and prompts using that atlas will have color as well.
I added a black drop shadow to all white text using this method.
I'd check out the fontbank folder and see if you can spot which one of the files that the promptlocal uses. Then add color in photoshop or any other image editing program.
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