Hi Andrew,
I have a bad habit of not documenting the steps I take. I just go with the flow from start to finish. Then when someone asks how I got there, I have to re-trace my very convoluted steps. So I apologize in advance for any frustration my methods cause anyone
I've gone over the steps you took...as long as the last layer (the original dupe, with no mask) is set to saturation, it should work. Just to clarify...here are the layers, from top (5) to bottom (1):
5 - Original dupe, set to saturation mode
4 - Original dupe with flower mask (blur the mask to taste, I think I used about 40-45)
3 - Hue/Sat layer (yes, everything turns white)
2 - Original, set to color dodge (yes, it will look awful at this point, be patient

) Also, on a second working of this, it seems you don't need to set it to color dodge at all, normal will still work. This detail doesn't change the outcome here however.
1 - Sketch layer
I'm thinking the problem might be the blurring of the flower mask on layer 4. The mask should look like 2 gray indistinct blobs. If it's too white, that allows too much of the original image through and it will seem as though there has been no change. Also, here's a tip that works with gradient masks...highlight the mask, then go to Image>Adjustments>Levels. Now move the middle slider back and forth and you can adjust the transition of the mask to make it harder or softer. You might want to try that on this layer.
I'm sending you the PSD file so you can take a look at the set-up first hand. Let me know how it goes....
Oooops, I didn't check your e-mail status first. If you'd like the file, just drop me an e-mail
Hope this helps a bit,
Pam