Recently we discussed what colour profile we use to print your images (Adobe RGB 1998), and why. Here is a visual reminder that the Adobe RGB 1998 colour space encompasses a much wider range of colours than does the SRGB colour space that most images use by default.
In this diagram, the coloured area represents visible colour, and the triangles inside it represent the range of colours within each colour space. It can be seen that more colours, especially at the blue/green end, are included in the Adobe RGB (1998) colour space than are included in the SRGB colour space. ProPhoto colour is another option, but you can see here that it extends beyond visible colour space, so choosing that profile can cause other problems that are hard to deal with.
So, when we print your image, what happens to the visible colours in that image that are not part of the selected colour profile? It is hard to determine what will happen without trying it, i.e. experimenting with printing. This is why we offer custom samples, and printed colour maps.
You can, however, check which of the colours within your image are not present in your selected colour profile. To do this, in Photoshop select View, Gamut Warning from the menu. Any colours that are outside of your selected colour profile will turn grey. Select View, Gamut Warning again to turn the warning off. Here is our colour map with the Gamut Warning on:
What can be done to have more control over your printed colour?
To take control of this issue, you could try changing those colours in your image that are not present in your colour profile to other colours that ARE present.
Or, just be aware that those colours that are not present in your colour profile may print in a way that you can not anticipate in advance, which is what sampling is for.
Oh, and then we print with a different, printer profile, which translates the Adobe RGB (1998) colour profile of the image to match what our printers are capable of! But luckily you do not need to worry about that.