There is indeed a way to do that, and I have a rule set up exactly like what you're talking about so that mail from anyone in my family shows up as orange on the list of messages rather than black. Definitely makes it jump out.

Here's how do set this up for yourself.

The easiest way to start is to move to a message from the person whom you want to have highlighted. Here's how it might look:

With that message still highlighted, you'll want to choose Tools --> Rules, which brings up:

I have a ton of rules, as you can see, but yours might be completely blank. Doesn't matter at this point. Just click on the "+ Add" on the top left, as highlighted above.

The Edit Rule window pops up with fairly useless default values:

Instead, let's give it a useful name (I'll choose "Highlight Important People") and change the condition from "All Messages" to "From". Entourage automatically fills in the return address of the message we've already selected (helpful!) and that is in fact the only test conditional we need. To have messages from that person change color, change the actions from "Change status" and "Set category" to be "Set category" (the options are a bunch of different colors, preset by Microsoft) and "Green", and "Change priority" and "Raise priority" as the value. Now it looks like this:

That's all we need to set up. If you have a lot of rules, you might want to drag and drop this new rule so it's at the top of the list: the rules are evaluated and executed in the order they appear on the list. Otherwise, you're good to go!

To test it, while that message is still selected, choose Message --> Apply Rule --> All Rules. In a second or two the message shoudl now change to be green (or whatever color you chose) in the message list and it should now be a priority message too.

I hope that'll ensure that your husband's email messages never get lost in your mailbox again. If green doesn't work, you can choose a brighter color. Even better, if you really want to get fancy, you can have Entourage pop up a small window with the message of your choice each time you get email from your spouse, friend or family member. Just choose "Display dialog" as one of the additional steps to execute on matching the rule you just created, and you'll have no excuses at all for not realizing that an important message has just arrived!