Blue eggs are a shell color. Brown eggs are actually a white shell with a brown pigment on them. To get a green egg it's a blue shell with the brown pigment on them, so depending on a variety of factors the egg color can range from green to blue depending on how much "ink" she has left.
As far as your question goes it depends on age and what you're feeding them. You tend to get the most irregularities when they first start laying: you'll get different colors, weird-shaped eggs, etc. If they start to molt they'll stop laying until they're done molting. Cream legbars aren't a production breed, so this time of year you're only likely to get an egg every other day from each hen, so if they're in "full swing" you'll see an egg every day most days with a pair of hens, and sometimes you'll either get none or two eggs in one day.