Some budgies can have a slight greenish hue to the normally orangish/yellow beak, depending on body color. If you post a clear pic(s), we can confirm if your bird has a normal appearance. Nutritional deficiencies present in other ways, not blue/green beak.
But regardless of seeing anything to question, please take a look at the Stickies in the diet and nutrition section (as well as all of the Stickies) if you haven’t already. There you will find guidelines to a well balanced diet for budgies.