This is one of the coloring pages newly made especially for The Day-by-Day Coloring Book of Saints, Volume 2, which contains saints for every single day of July through December. It's available here or from Amazon.
Melcizedek, Priest-King of Salem, offered bread and wine in a prefigurement of the Eucharist. Today is the Feast of the Precious Blood of Jesus! St. Melchizedek's day is August 26.