I'm not sure which process you're using. There are several ways.
For Antoinette's benefit, here's the address to the tutorial page on my website that explains the process I use and teach:
http://www.jimsdigitaldiary.com/colorizing.html
Actually I found the contrast to be fine on your B&W. But one tip to be aware of: whenever you do a color to B&W conversion (whatever method you choose), it's a good idea to re-check the Levels on the B&W. It sometimes needs to be readjusted.
Some people think this process - I call it "Colorizing" or "Selective Color" - has become trite and overused. But when well done it can be a very nice creative device.
I have an entire collection of what I've named "Escapes" on my Cafepress site. (Address in sig below) These are all flowers. And at least a part of each colored segment appears to be actually escaping the frame. You might find them interesting.