Grey (they're not blue) boxes result from someone trying to give you positive rep but they don't have enough positive rep themselves to do so.
1. The repper is new with no green boxes themselves.
2. The repper has red boxes.
What is the Reputation System? The Reputation System on the forums allows forum members to give and receive "Reputation" points to each other based on each others' posts. Did someone write a really killer guide to the Warforged class? Did another member help you out when you had a question? Give them props through the Reputation system! The higher your Reputation, and the longer you've been a forums member, the more power you have to raise (or lower) other players' Reputations!
How do I give Reputation? When you're looking at a post and want to give Reputation points to the poster, click on the Reputation icon, which looks like a pair of scales. You'll be asked if you approve or disapprove of the post; choose whichever you like, then click on "Add to Reputation."
How much Reputation can I give to other members? How much Reputation you can give (or take) depends on how long you've been a member of the forums and how much Reputation you have yourself!
How often can I give Reputation to another user? To prevent abuse of the system, you are limited to the number of Reputation clicks you can give in a single day, and you must give Reputation to a certain number of people before you can come back to someone you've given Reputation before. In essence, this means you cannot give any particular person Reputation more than once every few days.
I tried to give negative Reputation to a post I didn't like, but it wouldn't let me! You must have at least 1500 positive Reputation before you can give negative.
What does Reputation look like on the forums? When you have positive Reputation, it is displayed as green boxes. The boxes are grey if you have 0 Reputation, and red if you have negative Reputation.
What do I get for having Reputation? You'll earn Reputation titles based on your Reputation level - and the satisfaction of knowing your fellow members value your contributions to the forums! The Reputation Titles are viewable by hovering your mouse over a user's Reputation boxes.
Is there an easy way for me to see what Reputation I've received? Once you've received Reputation from other users, clicking on User CP will show you the last 10 Reputation clicks you've received and on which of your posts. You cannot see who left the Reputation.
What if I don't want to display my Reputation to other forum members? You can toggle whether your Reputation is displayed to other members by going to User CP -> Edit Options and checking or unchecking the "Show My Reputation Level" box.
How do I know how much Reputation I have? Clicking on User CP will show your Reputation level in two places: On the right side of the "Latest Reputation Received" box, and in the Options menu, under the "Show My Reputation Level" option.
What's the best way to gain Reputation? By posting useful, positive, or other posts your fellow community members like. Keep in mind that even if someone gives you negative Reputation for a post, it's your posts over time that will really decide how high or low your Reputation goes. Administrators will sometimes give Reputation for posts they find are particularly worthwhile.
What if I suspect abuse of the system? To report abuse of the Reputation system, please use the Report icon to report the post in which the abuse took place, or contact the moderation team through the Contact Us link at the bottom of the forums. Please note that members' use of the Reputation system must comply with the Code of Conduct and Forum Guidelines, and administrators are able to view the Reputation left for and by users. Users who are found to be abusing the Reputation system may have their own Reputation level altered at the discretion of the moderators.
What happens if a user's Reputation gets too low? If a user's Reputation goes below a certain threshold, they will automatically be moved to the Moderated usergroup, meaning all further posts will be placed in a moderation queue until the community team can review the circumstances and determine the correct course of action.
The review will include the user’s posting history, but will also make sure the user has not been “griefed” through the Reputation system by any individual or group.
http://support.turbine.com/link/portal/24001/24001/Article/192/DDO-Forums-FAQs