Even if you change the bulb to blue, the outcome is gonna be a mixture of blue and green. If you look at it closely you'll notice that the arrow template(outline) is green. I haven't tried this yet but if you wanna try cutting the arrow out, adhere a small piece of tint film to hide the modification combined with a blue bulb(or dip it in blue transparent paint). Better yet if you can find a piece of blue transparent plastic to cover the cut-out arrow, you wouldn't need a blue bulb. what do you think?