Where does any light come in?
I'd go for something warm so it doesn't look too cold if it doesn't attract much natural light and warms up the beech - something like a nice cream colour maybe with some uplighters to soften the light. You could always paint below the dado a darker shade to make more of an impact with the cream on top, like a nice warm chocolate brown colour, it will blend up from the floor then. Maybe even a pattern on the brown to drawn the attention upwards to the light, maybe a darker swirly pattern.