I just checked on another fruit, the skin/rind on it is thin, soft like a mandarin, it has a slight lemon taste but not really sour at all.
Millet, I do notice that of all the fruits on my multi-grafted tree, the NZ lemon rind does not turn fully yellow immediately, always seems to have some area that looks greenish on the side that is covered with leaves. When it gets fully yellow the rind is softer and almost seems too ripe to me. My fruits will look like the photos I showed (mostly yellow with some green area) while the other fruits such as the Sumo, Ponkan, Kiyomi, lemons all turn completely color (orange, yellow) even if they are partially covered by leaves.