First of all, lovely drawing! Your veins will be less pronounced, as they will take the value of the watercolor. But that is not necessarily a bad thing. As I see them now, they should be toned down a bit. Use a very lightly tinted hue and carefully brush over areas that you want the veins to be less pronounced. For example the side veins, particularly as they taper toward the margin of the leaf, and where the leaf goes into shadow.
I haven’t added watrcolor yet, when I do will I loose the white vein lines in the leaves? Not sure where the highlight would be?
First of all, lovely drawing! Your veins will be less pronounced, as they will take the value of the watercolor. But that is not necessarily a bad thing. As I see them now, they should be toned down a bit. Use a very lightly tinted hue and carefully brush over areas that you want the veins to be less pronounced. For example the side veins, particularly as they taper toward the margin of the leaf, and where the leaf goes into shadow.