Yea, the green shots are white/yellow to show they are 2 different shot types at the moment.
White is aimed at your screen pos, whereas yellow is a bit more clever; it is aimed at where you will be when it would hit you based on your speed when the shot was fired.
The colours and pretty much all the graphics are placeholders / aids for testing as opposed to the actual finished item.
With regards the cabinet, I will probably document the whole thing (I tend to do that with a lot of my projects) with all costs, plans and assorted fun along the way. I reckon (excluding the PC parts) you can do it for <£250 and considering I have been researching the thing for about 6 years now, it's about time I finally did it.
It does help that there is are good sources for the mechanical parts these days, so no need to delay any more!