It probably will make the pool warmer, but only by a degree or so. I don't have any facts to by this up but I do have a customer that is on there second black liner for this reason. I don't personally like the way the liner looks. It gets ashy looking quick and it seems that small imperfections behind the liner are more noticeable since there isn't a pattern to break it up. Regardless If you want to get warmer water I would look into solar heating, covers, etc. Get a liner that you think looks good for your yard. The only advice I would give you in picking a pattern is it seems that red and yellow inks fade the quickest with blue and greens lasting longer. Also if you have actual vinyl samples you'll notice one side of the sample has the liner print on it and the other side is blank. The blank side is the base color for the vinyl with inks printed on it to form a pattern. The reason why I think this is important is if the pattern is ever damaged or fades it will reveal the base color. For example if you have a dark blue base with dark blue inks that liner will look better in the long run than a white base with dark blue inks.
