See if they have an option in their system to turn off color correction. A lot of labs have these correction turned on because on average it helps everday peoples photos come out a little more punchy and less dark and lacking contrast. However, when printing something such as digital pages, it can wreck havoc as it will read the page and try to make colors different to match the "profile" that it has loaded. (i've had baby blues end up dark grey.....pinks end up white....black and whites end up green) Eseentially you are going to have the most problems on pages where there is a lot of contrast in the colors and items on the pages. Ask them about this and see if they can turn it off for you. It should just be a one click thing for them and it will make your prints come out much better (or at least matching each other). The actual color you end up with at that point is going to greatly depend on how well your monitor is calibrated to their printers.
yes...it does get confusing
-Kelly