When I used to use tissue to cover models, I used colored cellulose dope over a thinned clear dope surface.

After covering, spray with water and let dry to tighten the tissue, then apply a thinned coat of clear dope. This will make the tissue permanently tight, then apply as many slightly thinned colored coats as is necessary to get a solid color.

When covering, remember the tissue has a 'lay' to it. It tears easier in one direction than the other, and the easy tear direction should be across the smaller dimension of the part you are covering (that is, at 90 degrees to the length of the fuselage, and across the chord of the wing) so that the 'grain' runs parallel to the longer length.

-David C.