you know, i would typically berate an OP with a question of this type... BUT...

this is legitimate.

props OP for wanting to go about this the nice way... i understand that just because you love your wife unconditionally doesn't mean you will love every hair style she has.

i think the VERY best thing you can do all together is this:

Just ride it out this ONE time. don't compliment the hair, but don't talk it down, either. play it safe and just wait a couple months till the color starts to fade and she's needing to either get a cut or recolor and THEN and THEN ONLY you can maybe suggest a hairstyle you think looks good on her..

Say "honey, i think you really look sexy with ____"

or whatever.

That's it. That's all you can do. You're risking her getting some sort of complex if you say anything about it now, then you're risking her self-esteem, which then, in turn, will risk any kind of sexual encounter you may have wanted to have because you'll have to reassure her she's still attractive...

But if this hair cut is what I'm imagining... you may not want to have sexual contact with her for a while. lol

That's all. Legit question. Screw everyone else with their lame responses. This is a question you would read submitted to some magazine. This is the answer.