Any tattoo is, technically, doable. Yes, you could get a tattoo on your finger; yes, you could get an all white tattoo; yes, you could get tiny script along the arch of your foot. What you must ask yourself is if you're prepared for what it will look like six weeks, months, or years from now. When a tattoo artist tells you your idea won't work or that they won't do it, it isn't because they're lacking talent, it isn't because they fancy themselves the tattoo police, it's because they care about producing high-quality work, and they care about your satisfaction not just that day, but for years to come. Any tattoo shop could just take your money and give you the exact tattoo you asked for, but good shops will risk missing out on a little cash to ensure our clients are well-informed before making any permanent decisions - they will explain that ink spreads a little over time, so script done too small will be unreadable in a few years, and that fingers and parts of your feet won't hold ink the way other body parts will. Of course, what you end up deciding to get is completely up to you, but please, please keep in mind that if your artist has tried to talk you out of it, refused to do it, or insisted you make it bigger or put it somewhere else, it's not because they're a talentless jerk. It's because they care about you, your tattoos, and the artform as a whole.
Below are just a few examples of Pinterest ideas, and their real-world results.