That I don't know I only played through Colo once since I use it to transfer my 3rd gen mons as I lack a second gba t.t
However the answer in both games is to grind a lot with 2-3 mons 4 max. Espeon and Umbreon make a fantastic pair for battling and snagging but umbreon falls short at dealing damage by the end of the game, so you'll probably want to use croconaw and add flaaffy as it can spam T-Wave for easier catchs, despite being slow it has a lot of bulk and a thunderbolt from her is no joke either once she evolves.