Hardware - Wacom Intuos Tablet
Software - Paint Tool SAI

After Making the initial sketch I went on to make a cleaner version of the picture, all grayscale at this point.
I added as much detail as I could come up with in this stage as well, like the petals and how the lighting would behave.
Then I added a layer that acts as a colour-overlay and used this to come up with the colours.
Beyond that it was all detail-work and value-balancing.