Latius are very rare in the game!A latius colour is Red Or Blue.If you play pokemon ruby its red and if you play pokemon sapphire its blue.I dont know about pokemon emrald since i didnt play it.I cannot say you where you can get them in random but they come to you.Latius dont stay in one place they wander about so it depends about your luck if you sight them.Then they flee when you meet them give you only 1 chance for attacking or cattching.Ultra balls can't catch them nor any other ball.Only Master ball can catch them.So you have to save your master ball for catching it.Its upto you if you want catch the special pokemon that appears in pokemon runy,sapphire and emrald(eg:-groudon in pokemon ruby) or catch a latius!