go to home depot and look at their color charts and find a blue that you like. have them mix it up as a latex, and then yes you can roll it on. you might want to go a shade darker than you think at the counter, because intense lighting will make the paint look a tad lighter once you have it on the back of your tank.
as for "the best color blue" that is completely subjective, and depends a lot on what depth you are trying to recreate if you are trying to get technical.
HTH