U CAN USE BLACK MAGIC IMAGE COLOURISATION SOFTWARE.DOWNLOAD IT BY SEARCHING ON GOOGLE AS I DONT HAVE THE EXACT LINK.ITS EASY TO USE.
I have coloured few pics.I have done in Corel Photopaint.
1. Select An Area.
2.Add new mask
3. Fill The mask with colour.
4. Set opacity of the new mask as it seems to be the picture is already in colour.
Here are some samples.The Oxford university pic has been coloured using the BLACK MAGIC TOOL.