My suggestion is to talk to a few shops in your area and see If someone is willing to paint it and discuss it with them. There are shops that specialize in painting big rigs but not all custom paint. I work on semis where I work, but they don't do a lot of custom painting, most of the graphics and lettering are done in vinyl. They use mainly imron there since most semis get a lot of miles on the road and need a paint that is durable. Check around with a few shops and see if they will do that large of a project and do custome and get some references and ask about what kind of work they do. Maybe the right place can throw a few ideas together. As far as what to do is hard to say. What one person may like, another may hate. The possiblys are endless in paint and graphics, how far do you want to go and spend. There are all sorts of graphics (flames, scallops, ripped, ect, ect, ect and 3 stage flake, pearls and special effect paints if you really want to go wild and spend some money. House of kolors is probably one of the better known companys speciallizing in custom paint. hokpaint.com
Maybe you can visit your local paint supplier and start looking at some colors in chip books or custom paint chips if they handle that too. Keep in mind that the color you see in the books may not look exactly like it will when sprayed. Hopefuly it will be something your husband will like, what colors does he like, interests, did he ever mention he liked a certain color on a car or a certain paint job? Say he is a real big fan of fishing or something, maybe you could get part airbrushed with that theme. Or will he like a basic paint job or maybe something simple like a two tone. You kinda have to be the judge of what your husband would be interested in since this is a surprise for him. You can do a lot of searching on the internet and look at pictures for some inspiration, and read up on what different. Visiting custom motorcycle sites you can see what alot of custom finishes may look like, since these are often done with candy paint and graphics. So to some up all this rambling, someone can give you a suggestion on what they think will look cool, but its gotta be something you and your husband are going to like. I guess you have some thinking to do. Its tough deciding on paint. I have been looking for just the right color grey for a few weeks now and have to choose soon. Its much easier when you just have a paint code and go pick up the color you need. Also, I would be interested in how you plan on explaining why the truck is gone. Something that big, if going custom could take awhile to get done.