Thank you for reaching out to us.
Nail polish should be removed prior to immersion. Incomplete nail polish actually poses more halachic concerns than a complete manicure because women generally prefer to remove it. At the same time, women do not generally have a strong preference to remove traces of polish that are difficult to discern, and there is a halachic basis for extra leniency about toenail polish when women are less particular about toenails than fingernails. Therefore, while you should make an effort to remove all of the polish, you need not be concerned about traces such as you describe, and they do not invalidate immersion.
Two practical tips–You might find it helpful to remove the polish a day or two before mikveh, to ease time-pressure, and to use a Q-tip soaked in polish remover for hard to reach areas.
Please be in touch with any follow up questions.