How to do Gimp's colorize effect

Hi,

I am using ImageMagick for a couple of years, and I am very happy with it
:o)

Recently, I tried too generate text labels like the ones described in the
tutorial here: http://www.imagemagick.org/Usage/fonts/#bevel
Everything was nice until I tried to colorize them.

I successfuly masked my text, obtaining this image:
http://imagebin.ca/view/sHWTz7.html

Then I made some test in Gimp, and using Colors->Colorize with values:
- Hue: 297
- Saturation: 68
- Lightness: 40
I got this image which is more or less what I want:
http://imagebin.ca/view/NIe9_6.html

I then tried to achieve the same result with ImageMagick.
Since HSL(297,68,40) = RGB(99,33,102), I tried this:
convert _test5.png -fill rgb(99,33,102) -colorize 50% _testX.png

Result is very dark and far from perfect:
http://imagebin.ca/view/wjf1KN.html

I tried tweaking the colorize parameter, but I cannot get near the Gimp
result.

Is it a way to compute IM's colorize parameters from the Gimp's colorize
ones in order to get the same result?
I could go scriptfu here but I'd really like to learn a few more things with
ImageMagick :o)

Thanks for any hint!
Eric