The ballot initiatives proposed in Colorado are to legalize adult possession of marijuana for personal use. Small amounts. Under federal law that's a misdemeanor, not a felony.

The feds are not going to start charging people for possessing user quantities of marijuana unless its in conjunction with more serious charges, such as a person who is selling another drug and happens to have some pot on his person or in his vehicle or home. They simply don't have the resources and also aren't interested in bringing those cases. Federal prosecutors' guidelines set minimum threshold quantities in deciding whether to bring federal charges. While non-binding and there can be exceptions, in general, small drug possession cases involving user quantities are not brought in federal court in Colorado.

So for all intents and purposes, if Colorado voters pass the legalization measure in November, it will result in a lack of prosecution.

yes, cultivation is different. That's a felony, even for one plant under federal law. But again, from a practical standpoint, the feds aren't going to charge someone who just grows a few plants for his or her own use. As with other drug crimes, their policy guidelines provide minimum thresholds, they lack of resources and they aren't interested.

Possession of up to 1 ounce is now a petty offense in Colorado punishable by a $100 fine. But it also results in criminal record.  And it counts as a criminal history point if the person is later convicted of any federal offense, which increases their sentencing guidelines. (Only a few of our judges exempt it.)

Passing this initiative will result in Colorado not being able to charge and convict people of this offense. Coupled with the feds lack of interest and policy guidance against prosecuting small user cases,  many people will be able avoid a criminal record. And the lack of a state prosecution and conviction will also enable them to avoid the potential for a greater sentence if later convicted of any crime in federal court.

The feds past and present policy of not charging people in federal court solely with minor possession charges means these initiatives are likely to result in defacto legalization for users who don't also engage in more serious criminal conduct.

And what the he11 are they going to do if the voters make it legal in Colorado in November ?.

What I meant is what is the Fed going to do about the state's refusal to view M as illegal ?  While it might be technically illegal, the Feds will get zero cooperation from the Colorado authorities for M, which is going to be a nightmare for the Feds.