while getting the colours to match, if you're having problems because you can get one set to match but not the other on the same pic (like sky vs. sheds), look into try the history brush. -right below the regular brush, has a little swirl on it- what this'll do is paint what was 'once there', by selecting which step in the files history to paint from. If you can get one set of colours right once, and then get the other set right on the second try, select the older state in the history (there's a little empty icon next to each state), and "paint" over the area that you want to revert backwards... sounds complicated, but its an incredible tool. and if that isn't the case, well, heh, I dunno, just takin a guess is all. also, use all the tools if you aren't meaning the colour balance, curves, contrast, levels and saturation, all found in image-> adjust.