For Strawberry Vinegar, this issue should be alleviated somewhat, since you can choose between 5 different textboxes, and some of them are darker than the standard, which make the text pop more.
For AIdol, I can edit the text, but AIdol is a pretty old VN of mine and editing it isn't high on my priority list; not when I'm also working on a bunch of other projects atm. I'll try and get around to it at some point during the next couple of months, though.