First, if you want the snake, get him. But that is no pastel. Or its the lowest quality one I have ever seen. Pastels should be much brighter, cleaner, and redder than this animal.

Pastel is not genetic although it is often used to brighten certain other morphs. If this guy really is a pastel (although he really can not be referred to as such since he doesn't meet the requirements) he would not be capable of improving color.

Having said that, he still may be a very nice snake that you would enjoy having so the decision is ultimately up to you.