Determining if a trait is Mendelian
Sorry! It doesn't appear to be a Mendelian trait.
In order to be useful as a mendelian trait, people need to be able to figure out what is or is not expressing it, and what type of inheritance pattern it follows. Your answers do not fit with any of the three Mendelian inheritance patterns. It is possible that there is an on/off component, and it might help to rethink how you are identifying this trait.
In some cases an individual carrying a new trait might have other odd characteristics which can make it more difficult to isolate what you are breeding for. For example let's say you found an odd corn snake that has a rusty background color and a solid black belly instead of checkers, and started calling this a "rusty" corn. When breeding it the rusty background color might be absent in some, present in some, and at many levels between in each offspring you produce. Meanwhile the belly is either solid black or the normal checkered type. Using the original idea of rusty corns this appears not to be a Mendelian trait, but if you consider the belly pattern and the ground color separately, you can see that the solid belly is indeed a new on/off trait.
If you are unable to find any way to classify individuals as expressing or not expressing the trait, it is not Mendelian. This does not mean it isn't genetic or cannot be reproduced, it might be recovered through selective breeding, but it cannot be reproduced in the same ways as Mendelian traits are.