I'm not an expert, but as the former owner of a pair of '06 GTI SEs, I did a great deal of research on these models. My sister has a pair of '07s, which are very, very similar. I wanted to buy '07s, but couldn't find any. So, I ended up with '06s.
I came to the conclusion that this black hull was not part of the '06 lineup, but is for '07. The black hull came on the '07 SE. In '06, the "plain" GTI was white over white. The SE was blue over white. I haven't found anything to indicate if the 155 horse version had any color differences. I do know that in '07, the 155 had a gray cap instead of white.
'06:
White over white
Blue over white
'07:
White over white
White over black
Gray over black
Again, I'm not an authority, but this is the conclusion to which I came. Are you sure yours is not an '07?
I have looked and looked for a detailed listing of models, colors, and options for each year of Sea Doo PWC, but haven't found one. I've run across one or two that have some information, but are far from complete. I wonder if there are some year model brochures archived out there somewhere that show everything for given model years.