(がら) Used about flowers, plaid/stripes / zebra skin – wood. Very broad meaning. . . basically 柄 means. . .anything not plain!  Can be used about textures as well as pictures or colors, like blue wallpaper with sailboats on it is 柄. Unlike 模様、 柄 also has the nuance of ‘personality or characteristic.’  For instance, the wonderful word お国, which means the national character of a country.
(もよう) A pattern which does not have pictures: fractals, mandala, plaid, zebra skin. Wood-grain are all 模様. Do NOT use 模様 about representational patterns like flower-print or kids’ pajamas with horsies on them. 模様 also has a more formal meaning: ‘the details of an incident’, for example: A train/airport announcement which says “We will explain the details of the delay” (遅れるの模様.)
柄 and 模様. These two mean the same exact thing, but they are used in different situations. It’s really a case-by-case thing.