Re: texturing over paneling
The grooves are darker because the drywall compound is thicker in those areas and there could be some bleeding of the paneling in the grooves as well. Also, because the grooves are deeper, they will require more filling than skim coating because as the compound dries, it shrinks. You should use at least two coats of compound on the grooves. The joints between the panels will likely crack if you don't tape them with either paper or mesh joint tape. With two coats of primer and two coats of color, the lines should hide reasonably well.
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