With some pieces of furniture, typically pieces from the 1930s and 1940s, after painting the first coat there is either a yellow or pink stain which bleeds through the paint. No matter how may coats you paint, the stain colour will continue to bleed through.
The ANSWER is to get something called *Knotting or sometimes it is called shellac. Get the clear one and apply it using a pad rather than a brush. It dries in minutes and you can get on with painting immediately!
( *it's a natural product from an insect in South East Asia, using a resin depost that the insect extrudes to help them stick to trees. Strange but true!)