No, we can only print CMYK colors. It's on our roadmap to add support for RGB colors, but we do not know when this will be possible.
When artwork is submitted in RGB, the colors are converted to their closest available matches in CMYK before going to print. If you let us know your desired CMYK values when ordering it will make it easier for us to print your desired colors. Otherwise we will use our judgement to decide the closest equivalents.
Since RGB has a larger range of colors than CMYK, some RGB colors are currently difficult or impossible to match exactly.
Related FAQ: Why are some RGB colors difficult to match?