Colorless. Not only can it evolve turn 1, but it is also searchable by Winona, and due to the fact that Wally doesn't work on EXes, not to mention that so far, there's no card, whether in presently-legal expansions or known to be in any future expansion, that allows you to Mega Evolve any non-Colorless EX by any means, the dragon one is outclassed by the colorless version of M-Ray assuming the player goes second on turn 1 and attaches a Spirit Link to Ray-EX so that he can attack turn 1, due to the rule that states "the player that goes first on turn 1 cannot attack unless the description of the attack being used says otherwise"...
^ NOTE: Speaking of Winona, since she is a supporter card, if you want to make the first attack with M-Ray, an Ultra Ball would be a better choice for purposes of searching for M-Ray Colorless to achieve Turn 1 evolution, then, it's a matter of getting either one battle compressor + mega turbo + DCE, or two Mega Turbos + manual Energy attachment for turn, even if it requires a Sycamore to make it more likely to get the above, in order to meet that 3 CE requirement to use Colorless M-Ray's attack...
NOTE #2: Don't overlook the dragon version when trying to use emerald break: Assuming you don't draw Colorless M-Ray and a Sycamore and you go second, if you do not get a opponent mulligan boost to your hand, then unless your initial seven-card, minus Rayquaza-EX, hand consists of a battle compressor + vs seeker, then it's possible that either the emerald break will result in 0 damage due to no pokemon on bench, or if you have at least one pokemon on the bench, the Emerald Break could fall short of the magic 180 required to KO the Dragon Ray-EX on turn 1, both possibilities which also leave you vulnerable to a more likely, but still less probable, dragon Mega Ray-EX KO on turn 2 after Spirit link + 2 DDE + battle compressor + Mega Turbo, with 1-5+ less cards needed, to power up dragon M-Ray so it could meet the 5 energy req to use its 300 damage attack so that two prize cards against you will be drawn as a result of the colorless M-Ray getting KO'd... And if you have no pokemon on bench after that, that would mean game...