Hi. I did stuff like this for my helmet. You have a couple of options.
The easiest way is to have the eyes of the helmet filled in with a thin plastic (like PETG, very cheap and easy to work with at 0.02 thickness) that you apply coloration to. I did mine black, and I found that while dye worked it was messy and prone to failure by ending up gross looking and uneven. Window tint film,very easy to apply, turned out much better.
A quick google search confirms that white window tint is a thing. So 2-3 players of that, with at least one layer on each side of the plastic, and you should be good.
You might have to get more fancy if you want they eyes to light up, but I don't know if thats you plan anyway. If it is your plan, I *think* you just could go around the outside of the eye-plastic with some EL wire that lights up when you turn it on, and that *should* give you a light-up-eye effect without fucking blinding you. But I have not done that myself, so I cannot confirm.
Otherwise, instead of plastic, you can use a white mesh to fill in the eyes instead. Think like how those halloween grim reaper masks work, but a white cloth instead of a black one. I could not reccommend you a specific fabric for the task, as I have not done that.